Test two objects for inequality.
true if !(this == that), false otherwise.
Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.
a hash value consistent with ==
Construct a LazyList consisting of a given first element followed by elements from another LazyList.
Construct a LazyList consisting of the concatenation of the given LazyList and another LazyList.
Alias for concat
Alias for prependedAll
Alias for prepended.
Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.
Alias for appended
Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
true if the receiver object is equivalent to the argument; false otherwise.
Appends all elements of this lazy list to a string builder using start, end, and separator strings. The written text begins with the string start and ends with the string end. Inside, the string representations (w.r.t. the method toString) of all elements of this lazy list are separated by the string sep.
An undefined state is represented with "<not computed>" and cycles are represented with "<cycle>".
This method evaluates all elements of the collection.
the string builder to which elements are appended.
the starting string.
the separator string.
the ending string.
the string builder b to which elements were appended.
Appends all elements of this collection to a string builder. The written text consists of the string representations (w.r.t. the method toString) of all elements of this collection without any separator string.
Example:
scala> val a = List(1,2,3,4) a: List[Int] = List(1, 2, 3, 4) scala> val b = new StringBuilder() b: StringBuilder = scala> val h = a.addString(b) h: StringBuilder = 1234
the string builder to which elements are appended.
the string builder b to which elements were appended.
Appends all elements of this collection to a string builder using a separator string. The written text consists of the string representations (w.r.t. the method toString) of all elements of this collection, separated by the string sep.
Example:
scala> val a = List(1,2,3,4) a: List[Int] = List(1, 2, 3, 4) scala> val b = new StringBuilder() b: StringBuilder = scala> a.addString(b, ", ") res0: StringBuilder = 1, 2, 3, 4
the string builder to which elements are appended.
the separator string.
the string builder b to which elements were appended.
Composes this partial function with another partial function that gets applied to results of this partial function.
Note that calling isDefinedAt on the resulting partial function may apply the first partial function and execute its side effect. It is highly recommended to call applyOrElse instead of isDefinedAt / apply for efficiency.
the result type of the transformation function.
the transformation function
a partial function with the domain of this partial function narrowed by other partial function, which maps arguments x to k(this(x)).
Composes this partial function with a transformation function that gets applied to results of this partial function.
If the runtime type of the function is a PartialFunction then the other andThen method is used (note its cautions).
the result type of the transformation function.
the transformation function
a partial function with the domain of this partial function, possibly narrowed by the specified function, which maps arguments x to k(this(x)).
A copy of this lazy list with an element appended.
Note: will not terminate for infinite-sized collections.
Example:
scala> val a = List(1) a: List[Int] = List(1) scala> val b = a :+ 2 b: List[Int] = List(1, 2) scala> println(a) List(1)
This method preserves laziness; elements are only evaluated individually as needed.
Note: Repeated chaining of calls to append methods (appended, appendedAll, lazyAppendedAll) without forcing any of the intermediate resulting lazy lists may overflow the stack when the final result is forced.
the element type of the returned lazy list.
the appended element
a new lazy list consisting of all elements of this lazy list followed by value.
Returns a new lazy list containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the lazy list is the most specific superclass encompassing the element types of the two operands.
This method preserves laziness; elements are only evaluated individually as needed.
Note: Repeated chaining of calls to append methods (appended, appendedAll, lazyAppendedAll) without forcing any of the intermediate resulting lazy lists may overflow the stack when the final result is forced.
the element type of the returned collection.
the iterable to append.
a new collection of type CC[B] which contains all elements of this lazy list followed by all elements of suffix.
Get the element at the specified index. This operation is provided for convenience in Seq. It should not be assumed to be efficient unless you have an IndexedSeq.
Applies this partial function to the given argument when it is contained in the function domain. Applies fallback function where this partial function is not defined.
Note that expression pf.applyOrElse(x, default) is equivalent to
if(pf isDefinedAt x) pf(x) else default(x)
except that applyOrElse method can be implemented more efficiently. For all partial function literals the compiler generates an applyOrElse implementation which avoids double evaluation of pattern matchers and guards. This makes applyOrElse the basis for the efficient implementation for many operations and scenarios, such as:
orElse/andThen chains does not lead to excessive apply/isDefinedAt evaluation
lift and unlift do not evaluate source functions twice on each invocation
runWith allows efficient imperative-style combining of partial functions with conditionally applied actions For non-literal partial function classes with nontrivial isDefinedAt method it is recommended to override applyOrElse with custom implementation that avoids double isDefinedAt evaluation. This may result in better performance and more predictable behavior w.r.t. side effects.
the function argument
the fallback function
the result of this function or fallback function application.
2.10
Cast the receiver object to be of type T0.
Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.
the receiver object.
ClassCastException if the receiver object is not an instance of the erasure of type T0.
Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.
The object with which this sequence should be compared
true, if this sequence can possibly equal that, false otherwise. The test takes into consideration only the run-time types of objects but ignores their elements.
Defines the prefix of this object's toString representation.
It is recommended to return the name of the concrete collection type, but not implementation subclasses. For example, for ListMap this method should return "ListMap", not "Map" (the supertype) or "Node" (an implementation subclass).
The default implementation returns "Iterable". It is overridden for the basic collection kinds "Seq", "IndexedSeq", "LinearSeq", "Buffer", "Set", "Map", "SortedSet", "SortedMap" and "View".
a string representation which starts the result of toString applied to this lazy list. By default the string prefix is the simple name of the collection class lazy list.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
a copy of the receiver object.
This collection as a C.
Builds a new lazy list by applying a partial function to all elements of this lazy list on which the function is defined.
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the returned lazy list.
the partial function which filters and maps the lazy list.
a new lazy list resulting from applying the given partial function pf to each element on which it is defined and collecting the results. The order of the elements is preserved.
Finds the first element of the lazy list for which the given partial function is defined, and applies the partial function to it.
Note: may not terminate for infinite-sized collections.
This method does not evaluate any elements further than the first element for which the partial function is defined.
the partial function
an option value containing pf applied to the first value for which it is defined, or None if none exists.
Iterates over combinations. A _combination_ of length n is a subsequence of the original sequence, with the elements taken in order. Thus, "xy" and "yy" are both length-2 combinations of "xyy", but "yx" is not. If there is more than one way to generate the same subsequence, only one will be returned.
For example, "xyyy" has three different ways to generate "xy" depending on whether the first, second, or third "y" is selected. However, since all are identical, only one will be chosen. Which of the three will be taken is an implementation detail that is not defined.
Note: Even when applied to a view or a lazy collection it will always force the elements.
An Iterator which traverses the possible n-element combinations of this sequence.
"abbbc".combinations(2) = Iterator(ab, ac, bb, bc)
Composes another partial function k with this partial function so that this partial function gets applied to results of k.
Note that calling isDefinedAt on the resulting partial function may apply the first partial function and execute its side effect. It is highly recommended to call applyOrElse instead of isDefinedAt / apply for efficiency.
the parameter type of the transformation function.
the transformation function
a partial function with the domain of other partial function narrowed by this partial function, which maps arguments x to this(k(x)).
Composes two instances of Function1 in a new Function1, with this function applied last.
the type to which function g can be applied
a function A => T1
a new function f such that f(x) == apply(g(x))
Returns a new sequence containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the sequence is the most specific superclass encompassing the element types of the two operands.
the element type of the returned collection.
the traversable to append.
a new sequence which contains all elements of this sequence followed by all elements of suffix.
Tests whether this sequence contains a given value as an element.
Note: may not terminate for infinite-sized collections.
the element to test.
true if this sequence has an element that is equal (as determined by ==) to elem, false otherwise.
Tests whether this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
the sequence to test
true if this sequence contains a slice with the same elements as that, otherwise false.
Copy elements to an array, returning the number of elements written.
Fills the given array xs starting at index start with at most len elements of this collection.
Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached, or len elements have been copied.
the type of the elements of the array.
the array to fill.
the starting index of xs.
the maximal number of elements to copy.
the number of elements written to the array
Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change. Note: will not terminate for infinite-sized collections.
Copy elements to an array, returning the number of elements written.
Fills the given array xs starting at index start with values of this collection.
Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.
the type of the elements of the array.
the array to fill.
the starting index of xs.
the number of elements written to the array Note: will not terminate for infinite-sized collections.
Copy elements to an array, returning the number of elements written.
Fills the given array xs starting at index start with values of this collection.
Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.
the type of the elements of the array.
the array to fill.
the number of elements written to the array Note: will not terminate for infinite-sized collections.
Tests whether every element of this sequence relates to the corresponding element of another sequence by satisfying a test predicate.
the type of the elements of that
the other sequence
the test predicate, which relates elements from both sequences
true if both sequences have the same length and p(x, y) is true for all corresponding elements x of this sequence and y of that, otherwise false.
Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.
the type of the elements of that
the other collection
the test predicate, which relates elements from both collections
true if both collections have the same length and p(x, y) is true for all corresponding elements x of this iterator and y of that, otherwise false
Counts the number of elements in the collection which satisfy a predicate.
the predicate used to test elements.
the number of elements satisfying the predicate p.
Computes the multiset difference between this lazy list and another sequence.
This method preserves laziness; elements are only evaluated individually as needed.
the sequence of elements to remove
a new lazy list which contains all elements of this lazy list except some of occurrences of elements that also appear in that. If an element value x appears n times in that, then the first n occurrences of x will not form part of the result, but any following occurrences will.
Selects all the elements of this sequence ignoring the duplicates.
a new sequence consisting of all the elements of this sequence without duplicates.
Selects all the elements of this sequence ignoring the duplicates as determined by == after applying the transforming function f.
the type of the elements after being transformed by f
The transforming function whose result is used to determine the uniqueness of each element
a new sequence consisting of all the elements of this sequence without duplicates.
Selects all elements except first n ones.
This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty). Additionally, it preserves laziness for all except the first n elements.
the number of elements to drop from this lazy list.
a lazy list consisting of all elements of this lazy list except the first n ones, or else the empty lazy list, if this lazy list has less than n elements. If n is negative, don't drop any elements.
Selects all elements except last n ones.
This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty).
the number of elements to drop from this lazy list.
a lazy list consisting of all elements of this lazy list except the last n ones, or else the empty lazy list, if this lazy list has less than n elements. If n is negative, don't drop any elements.
Drops longest prefix of elements that satisfy a predicate.
This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty). Additionally, it preserves laziness for all elements after the predicate returns false.
The predicate used to test elements.
the longest suffix of this lazy list whose first element does not satisfy the predicate p.
Returns an extractor object with a unapplySeq method, which extracts each element of a sequence data.
val firstChar: String => Option[Char] = _.headOption
Seq("foo", "bar", "baz") match {
case firstChar.unlift.elementWise(c0, c1, c2) =>
println(s"$c0, $c1, $c2") // Output: f, b, b
}
The empty iterable of the same type as this iterable
an empty iterable of type C.
Tests whether this sequence ends with the given sequence.
Note: will not terminate for infinite-sized collections.
the sequence to test
true if this sequence has that as a suffix, false otherwise.
Tests whether the argument (that) is a reference to the receiver object (this).
The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:
x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
null.eq(null) returns true. When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).
true if the argument is a reference to the receiver object; false otherwise.
The universal equality method defined in AnyRef.
This method evaluates all elements of the collection.
Tests whether a predicate holds for at least one element of this sequence.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
true if the given predicate p is satisfied by at least one element of this sequence, otherwise false
Selects all elements of this lazy list which satisfy a predicate.
This method preserves laziness; elements are only evaluated individually as needed.
a new iterator consisting of all elements of this lazy list that satisfy the given predicate p. The order of the elements is preserved.
Selects all elements of this lazy list which do not satisfy a predicate.
This method preserves laziness; elements are only evaluated individually as needed.
the predicate used to test elements.
a new lazy list consisting of all elements of this lazy list that do not satisfy the given predicate pred. Their order may not be preserved.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.
Finds the first element of the lazy list satisfying a predicate, if any.
Note: may not terminate for infinite-sized collections.
This method does not evaluate any elements further than the first element matching the predicate.
the predicate used to test elements.
an option value containing the first element in the lazy list that satisfies p, or None if none exists.
Finds the last element of the sequence satisfying a predicate, if any.
Note: will not terminate for infinite-sized collections.
the predicate used to test elements.
an option value containing the last element in the sequence that satisfies p, or None if none exists.
Builds a new lazy list by applying a function to all elements of this lazy list and using the elements of the resulting collections.
For example:
def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")
The type of the resulting collection is guided by the static type of lazy list. This might cause unexpected results sometimes. For example:
// lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set
def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet)
// lettersOf will return a Set[Char], not a Seq
def lettersOf(words: Seq[String]) = words.toSet flatMap ((word: String) => word.toSeq)
// xs will be an Iterable[Int]
val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2)
// ys will be a Map[Int, Int]
val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the returned collection.
the function to apply to each element.
a new lazy list resulting from applying the given collection-valued function f to each element of this lazy list and concatenating the results.
Converts this lazy list of traversable collections into a lazy list formed by the elements of these traversable collections.
The resulting collection's type will be guided by the type of lazy list. For example:
val xs = List(
Set(1, 2, 3),
Set(1, 2, 3)
).flatten
// xs == List(1, 2, 3, 1, 2, 3)
val ys = Set(
List(1, 2, 3),
List(3, 2, 1)
).flatten
// ys == Set(1, 2, 3)
This method preserves laziness; elements are only evaluated individually as needed.
the type of the elements of each traversable collection.
an implicit conversion which asserts that the element type of this lazy list is a GenTraversable.
a new lazy list resulting from concatenating all element lazy lists.
Folds the elements of this collection using the specified associative binary operator. The default implementation in IterableOnce is equivalent to foldLeft but may be overridden for more efficient traversal orders.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
Note: will not terminate for infinite-sized collections.
a type parameter for the binary operator, a supertype of A.
a neutral element for the fold operation; may be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for list concatenation, 0 for addition, or 1 for multiplication).
a binary operator that must be associative.
the result of applying the fold operator op between all the elements and z, or z if this collection is empty.
LazyList specialization of foldLeft which allows GC to collect along the way.
The type of value being accumulated.
The initial value seeded into the function op.
The operation to perform on successive elements of the LazyList.
The accumulated value from successive applications of op.
Applies a binary operator to all elements of this collection and a start value, going right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op between consecutive elements of this collection, going right to left with the start value z on the right:
op(x_1, op(x_2, ... op(x_n, z)...))
where x1, ..., xn are the elements of this collection. Returns z if this collection is empty.
Tests whether a predicate holds for all elements of this sequence.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
true if this sequence is empty or the given predicate p holds for all elements of this sequence, otherwise false.
Evaluates all undefined elements of the lazy list.
This method detects cycles in lazy lists, and terminates after all elements of the cycle are evaluated. For example:
val ring: LazyList[Int] = 1 #:: 2 #:: 3 #:: ring ring.force ring.toString // prints // // LazyList(1, 2, 3, ...)
This method will *not* terminate for non-cyclic infinite-sized collections.
this
Apply the given function f to each element of this linear sequence (while respecting the order of the elements).
The treatment to apply to each element.
Overridden here as final to trigger tail-call optimization, which replaces 'this' with 'tail' at each iteration. This is absolutely necessary for allowing the GC to collect the underlying LazyList as elements are consumed.
,This function will force the realization of the entire LazyList unless the f throws an exception.
Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).
Defines how to turn a given Iterable[A] into a collection of type C.
This process can be done in a strict way or a non-strict way (ie. without evaluating the elements of the resulting collections). In other words, this methods defines the evaluation model of the collection.
When implementing a custom collection type and refining C to the new type, this method needs to be overridden (the compiler will issue an error otherwise). In the common case where C =:= CC[A], this can be done by mixing in the IterableFactoryDefaults trait, which implements the method using iterableFactory.
As witnessed by the @uncheckedVariance annotation, using this method might be unsound. However, as long as it is called with an Iterable[A] obtained from this collection (as it is the case in the implementations of operations where we use a View[A]), it is safe.
Returns the runtime class representation of the object.
a class object corresponding to the runtime type of the receiver.
Partitions this iterable collection into a map of iterable collections according to some discriminator function.
Note: Even when applied to a view or a lazy collection it will always force the elements.
the type of keys returned by the discriminator function.
the discriminator function.
A map from keys to iterable collections such that the following invariant holds:
(xs groupBy f)(k) = xs filter (x => f(x) == k)
That is, every key k is bound to a iterable collection of those elements x for which f(x) equals k.
Partitions this iterable collection into a map of iterable collections according to a discriminator function key. Each element in a group is transformed into a value of type B using the value function.
It is equivalent to groupBy(key).mapValues(_.map(f)), but more efficient.
case class User(name: String, age: Int) def namesByAge(users: Seq[User]): Map[Int, Seq[String]] = users.groupMap(_.age)(_.name)
Note: Even when applied to a view or a lazy collection it will always force the elements.
the type of keys returned by the discriminator function
the type of values returned by the transformation function
the discriminator function
the element transformation function
Partitions this iterable collection into a map according to a discriminator function key. All the values that have the same discriminator are then transformed by the value function and then reduced into a single value with the reduce function.
It is equivalent to groupBy(key).mapValues(_.map(f).reduce(reduce)), but more efficient.
def occurrences[A](as: Seq[A]): Map[A, Int] = as.groupMapReduce(identity)(_ => 1)(_ + _)
Note: Even when applied to a view or a lazy collection it will always force the elements.
Partitions elements in fixed size lazy lists.
The iterator returned by this method mostly preserves laziness; a single element ahead of the iterator is evaluated.
the number of elements per group
An iterator producing lazy lists of size size, except the last will be less than size size if the elements don't divide evenly.
The hashCode method for reference types. See hashCode in scala.Any.
the hash code value for this object.
Selects the first element of this lazy list.
the first element of this lazy list.
NoSuchElementException if the lazy list is empty.
Optionally selects the first element.
the first element of this sequence if it is nonempty, None if it is empty.
Finds index of first occurrence of some value in this sequence.
the type of the element elem.
the element value to search for.
the index >= 0 of the first element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.
Finds index of first occurrence of some value in this sequence after or at some start index.
the type of the element elem.
the element value to search for.
the start index
the index >= from of the first element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.
Finds first index where this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
the sequence to test
the first index >= 0 such that the elements of this sequence starting at this index match the elements of sequence that, or -1 of no such subsequence exists.
Finds first index after or at a start index where this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
the sequence to test
the start index
the first index >= from such that the elements of this sequence starting at this index match the elements of sequence that, or -1 of no such subsequence exists.
Finds index of the first element satisfying some predicate after or at some start index.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the start index
the index >= from of the first element of this sequence that satisfies the predicate p, or -1, if none exists.
Finds index of the first element satisfying some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the index >= 0 of the first element of this sequence that satisfies the predicate p, or -1, if none exists.
Produces the range of all indices of this sequence.
Note: Even when applied to a view or a lazy collection it will always force the elements.
a Range value from 0 to one less than the length of this sequence.
The initial part of the collection without its last element.
Note: Even when applied to a view or a lazy collection it will always force the elements.
Iterates over the inits of this iterable collection. The first value will be this iterable collection and the final one will be an empty iterable collection, with the intervening values the results of successive applications of init.
Note: Even when applied to a view or a lazy collection it will always force the elements.
an iterator over all the inits of this iterable collection
List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)
Computes the multiset intersection between this lazy list and another sequence.
This method preserves laziness; elements are only evaluated individually as needed.
the sequence of elements to intersect with.
a new lazy list which contains all elements of this lazy list which also appear in that. If an element value x appears n times in that, then the first n occurrences of x will be retained in the result, but any following occurrences will be omitted.
Tests whether this sequence contains given index.
The implementations of methods apply and isDefinedAt turn a Seq[A] into a PartialFunction[Int, A].
true if this sequence contains an element at position idx, false otherwise.
Tests whether the lazy list is empty.
Note: Implementations in subclasses that are not repeatedly traversable must take care not to consume any elements when isEmpty is called.
true if the lazy list contains no elements, false otherwise.
Test whether the dynamic type of the receiver object is T0.
Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.
true if the receiver object is an instance of erasure of type T0; false otherwise.
Tests whether this iterable collection can be repeatedly traversed. Always true for Iterables and false for Iterators unless overridden.
true if it is repeatedly traversable, false otherwise.
The companion object of this lazy list, providing various factory methods.
Iterator can be used only once
The iterator returned by this method preserves laziness; elements are only evaluated individually as needed.
This method preserves laziness; elements are only evaluated individually as needed.
The number of elements in this lazy list, if it can be cheaply computed, -1 otherwise. Cheaply usually means: Not requiring a collection traversal.
Selects the last element.
The last element of this sequence.
NoSuchElementException If the sequence is empty.
Finds index of last occurrence of some value in this sequence before or at a given end index.
Note: will not terminate for infinite-sized collections.
the type of the element elem.
the element value to search for.
the end index.
the index <= end of the last element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.
Finds last index where this sequence contains a given sequence as a slice.
Note: will not terminate for infinite-sized collections.
the sequence to test
the last index such that the elements of this sequence starting at this index match the elements of sequence that, or -1 of no such subsequence exists.
Finds last index before or at a given end index where this sequence contains a given sequence as a slice.
Note: will not terminate for infinite-sized collections.
the sequence to test
the end index
the last index <= end such that the elements of this sequence starting at this index match the elements of sequence that, or -1 of no such subsequence exists.
Finds index of last element satisfying some predicate before or at given end index.
Note: will not terminate for infinite-sized collections.
the predicate used to test elements.
the index <= end of the last element of this sequence that satisfies the predicate p, or -1, if none exists.
Finds index of last element satisfying some predicate.
Note: will not terminate for infinite-sized collections.
the predicate used to test elements.
the index of the last element of this sequence that satisfies the predicate p, or -1, if none exists.
Optionally selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the last element of this iterable collection$ if it is nonempty, None if it is empty.
The lazy list resulting from the concatenation of this lazy list with the argument lazy list.
This method preserves laziness; elements are only evaluated individually as needed.
Note: Repeated chaining of calls to append methods (appended, appendedAll, lazyAppendedAll) without forcing any of the intermediate resulting lazy lists may overflow the stack when the final result is forced.
The collection that gets appended to this lazy list
The lazy list containing elements of this lazy list and the iterable object.
Analogous to zip except that the elements in each collection are not consumed until a strict operation is invoked on the returned LazyZip2 decorator.
Calls to lazyZip can be chained to support higher arities (up to 4) without incurring the expense of constructing and deconstructing intermediary tuples.
val xs = List(1, 2, 3) val res = (xs lazyZip xs lazyZip xs lazyZip xs).map((a, b, c, d) => a + b + c + d) // res == List(4, 8, 12)
This method is not particularly useful for a lazy list, as zip already preserves laziness.
The collection.LazyZip2 returned by this method preserves laziness; elements are only evaluated individually as needed.
the type of the second element in each eventual pair
the iterable providing the second element of each eventual pair
a decorator LazyZip2 that allows strict operations to be performed on the lazily evaluated pairs or chained calls to lazyZip. Implicit conversion to Iterable[(A, B)] is also supported.
The length (number of elements) of the sequence. size is an alias for length in Seq collections.
Compares the length of this sequence to the size of another Iterable.
the Iterable whose size is compared with this sequence's length.
A value x where
x < 0 if this.length < that.size x == 0 if this.length == that.size x > 0 if this.length > that.size
The method as implemented here does not call length or size directly; its running time is O(this.length min that.size) instead of O(this.length + that.size). The method should be overridden if computing size is cheap and knownSize returns -1.
Compares the length of this sequence to a test value.
the test value that gets compared with the length.
A value x where
x < 0 if this.length < len x == 0 if this.length == len x > 0 if this.length > len
The method as implemented here does not call length directly; its running time is O(length min len) instead of O(length). The method should be overridden if computing length is cheap and knownSize returns -1.
Returns a value class containing operations for comparing the length of this sequence to a test value.
These operations are implemented in terms of lengthCompare(Int), and allow the following more readable usages:
this.lengthIs < len // this.lengthCompare(len) < 0 this.lengthIs <= len // this.lengthCompare(len) <= 0 this.lengthIs == len // this.lengthCompare(len) == 0 this.lengthIs != len // this.lengthCompare(len) != 0 this.lengthIs >= len // this.lengthCompare(len) >= 0 this.lengthIs > len // this.lengthCompare(len) > 0
Turns this partial function into a plain function returning an Option result.
a function that takes an argument x to Some(this(x)) if this is defined for x, and to None otherwise.
Function.unlift
Builds a new lazy list by applying a function to all elements of this lazy list.
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the returned lazy list.
the function to apply to each element.
a new lazy list resulting from applying the given function f to each element of this lazy list and collecting the results.
Finds the largest element.
The type over which the ordering is defined.
An ordering to be used for comparing elements.
the largest element of this collection with respect to the ordering ord.
UnsupportedOperationException if this collection is empty.
Finds the first element which yields the largest value measured by function f.
The result type of the function f.
The measuring function.
An ordering to be used for comparing elements.
the first element of this collection with the largest value measured by function f with respect to the ordering cmp.
UnsupportedOperationException if this collection is empty.
Finds the first element which yields the largest value measured by function f.
The result type of the function f.
The measuring function.
An ordering to be used for comparing elements.
an option value containing the first element of this collection with the largest value measured by function f with respect to the ordering cmp.
Finds the largest element.
The type over which the ordering is defined.
An ordering to be used for comparing elements.
an option value containing the largest element of this collection with respect to the ordering ord.
Finds the smallest element.
The type over which the ordering is defined.
An ordering to be used for comparing elements.
the smallest element of this collection with respect to the ordering ord.
UnsupportedOperationException if this collection is empty.
Finds the first element which yields the smallest value measured by function f.
The result type of the function f.
The measuring function.
An ordering to be used for comparing elements.
the first element of this collection with the smallest value measured by function f with respect to the ordering cmp.
UnsupportedOperationException if this collection is empty.
Finds the first element which yields the smallest value measured by function f.
The result type of the function f.
The measuring function.
An ordering to be used for comparing elements.
an option value containing the first element of this collection with the smallest value measured by function f with respect to the ordering cmp.
Finds the smallest element.
The type over which the ordering is defined.
An ordering to be used for comparing elements.
an option value containing the smallest element of this collection with respect to the ordering ord.
Displays all elements of this collection in a string.
Delegates to addString, which can be overridden.
a string representation of this collection. In the resulting string the string representations (w.r.t. the method toString) of all elements of this collection follow each other without any separator string.
Displays all elements of this collection in a string using a separator string.
Delegates to addString, which can be overridden.
the separator string.
a string representation of this collection. In the resulting string the string representations (w.r.t. the method toString) of all elements of this collection are separated by the string sep.
List(1, 2, 3).mkString("|") = "1|2|3"
Displays all elements of this collection in a string using start, end, and separator strings.
Delegates to addString, which can be overridden.
the starting string.
the separator string.
the ending string.
a string representation of this collection. The resulting string begins with the string start and ends with the string end. Inside, the string representations (w.r.t. the method toString) of all elements of this collection are separated by the string sep.
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
Equivalent to !(this eq that).
true if the argument is not a reference to the receiver object; false otherwise.
a strict builder for the same collection type. Note that in the case of lazy collections (e.g. View or immutable.LazyList), it is possible to implement this method but the resulting Builder will break laziness. As a consequence, operations should preferably be implemented with fromSpecific instead of this method.
When implementing a custom collection type and refining C to the new type, this method needs to be overridden (the compiler will issue an error otherwise). In the common case where C =:= CC[A], this can be done by mixing in the IterableFactoryDefaults trait, which implements the method using iterableFactory.
As witnessed by the @uncheckedVariance annotation, using this method might be unsound. However, as long as the returned builder is only fed with A values taken from this instance, it is safe.
Tests whether the collection is not empty.
true if the collection contains at least one element, false otherwise.
Wakes up a single thread that is waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Wakes up all threads that are waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.
the argument type of the fallback function
the result type of the fallback function
the fallback function
a partial function which has as domain the union of the domains of this partial function and that. The resulting partial function takes x to this(x) where this is defined, and to that(x) where it is not.
A copy of this lazy list with an element value appended until a given target length is reached.
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the returned lazy list.
the target length
the padding value
a new lazy list consisting of all elements of this lazy list followed by the minimal number of occurrences of elem so that the resulting collection has a length of at least len.
A pair of, first, all elements that satisfy predicate p and, second, all elements that do not. Interesting because it splits a collection in two.
The default implementation provided here needs to traverse the collection twice. Strict collections have an overridden version of partition in StrictOptimizedIterableOps, which requires only a single traversal.
This method preserves laziness; elements are only evaluated individually as needed.
Applies a function f to each element of the lazy list and returns a pair of lazy lists: the first one made of those values returned by f that were wrapped in scala.util.Left, and the second one made of those wrapped in scala.util.Right.
Example:
val xs = `LazyList`(1, "one", 2, "two", 3, "three") partitionMap {
case i: Int => Left(i)
case s: String => Right(s)
}
// xs == (`LazyList`(1, 2, 3),
// `LazyList`(one, two, three))
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the first resulting collection
the element type of the second resulting collection
the 'split function' mapping the elements of this lazy list to an scala.util.Either
a pair of lazy lists: the first one made of those values returned by f that were wrapped in scala.util.Left, and the second one made of those wrapped in scala.util.Right.
Produces a new lazy list where a slice of elements in this lazy list is replaced by another sequence.
Patching at negative indices is the same as patching starting at 0. Patching at indices at or larger than the length of the original lazy list appends the patch to the end. If more values are replaced than actually exist, the excess is ignored.
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the returned lazy list.
the index of the first replaced element
the replacement sequence
the number of elements to drop in the original lazy list
a new lazy list consisting of all elements of this lazy list except that replaced elements starting from from are replaced by all the elements of other.
Iterates over distinct permutations.
Note: Even when applied to a view or a lazy collection it will always force the elements.
An Iterator which traverses the distinct permutations of this sequence.
"abb".permutations = Iterator(abb, bab, bba)
A copy of the lazy list with an element prepended.
Also, the original lazy list is not modified, so you will want to capture the result.
Example:
scala> val x = List(1) x: List[Int] = List(1) scala> val y = 2 +: x y: List[Int] = List(2, 1) scala> println(x) List(1)
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the returned lazy list.
the prepended element
a new lazy list consisting of value followed by all elements of this lazy list.
As with :++, returns a new collection containing the elements from the left operand followed by the elements from the right operand.
It differs from :++ in that the right operand determines the type of the resulting collection rather than the left one. Mnemonic: the COLon is on the side of the new COLlection type.
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the returned collection.
the iterable to prepend.
a new lazy list which contains all elements of prefix followed by all the elements of this lazy list.
Multiplies up the elements of this collection.
the result type of the * operator.
an implicit parameter defining a set of numeric operations which includes the * operator to be used in forming the product.
the product of all elements of this collection with respect to the * operator in num.
Reduces the elements of this collection using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
A type parameter for the binary operator, a supertype of A.
A binary operator that must be associative.
The result of applying reduce operator op between all the elements if the collection is nonempty.
UnsupportedOperationException if this collection is empty.
LazyList specialization of reduceLeft which allows GC to collect along the way.
The type of value being accumulated.
The operation to perform on successive elements of the LazyList.
The accumulated value from successive applications of f.
Optionally applies a binary operator to all elements of this collection, going left to right.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceLeft(op) if this collection is nonempty, None otherwise.
Reduces the elements of this collection, if any, using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
A type parameter for the binary operator, a supertype of A.
A binary operator that must be associative.
An option value containing result of applying reduce operator op between all the elements if the collection is nonempty, and None otherwise.
Applies a binary operator to all elements of this collection, going right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.
the result type of the binary operator.
the binary operator.
the result of inserting op between consecutive elements of this collection, going right to left:
op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))
where x1, ..., xn are the elements of this collection.
UnsupportedOperationException if this collection is empty.
Optionally applies a binary operator to all elements of this collection, going right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceRight(op) if this collection is nonempty, None otherwise.
Returns new lazy list with elements in reversed order.
Note: will not terminate for infinite-sized collections.
Note: Even when applied to a view or a lazy collection it will always force the elements.
This method evaluates all elements of the collection.
A new lazy list with all elements of this lazy list in reversed order.
An iterator yielding elements in reversed order.
Note: will not terminate for infinite-sized collections.
Note: xs.reverseIterator is the same as xs.reverse.iterator but might be more efficient.
an iterator yielding the elements of this sequence in reversed order
Composes this partial function with an action function which gets applied to results of this partial function. The action function is invoked only for its side effects; its result is ignored.
Note that expression pf.runWith(action)(x) is equivalent to
if(pf isDefinedAt x) { action(pf(x)); true } else false
except that runWith is implemented via applyOrElse and thus potentially more efficient. Using runWith avoids double evaluation of pattern matchers and guards for partial function literals.
the action function
a function which maps arguments x to isDefinedAt(x). The resulting function runs action(this(x)) where this is defined.
2.10
applyOrElse.
Are the elements of this collection the same (and in the same order) as those of that?
Computes a prefix scan of the elements of the collection.
Note: The neutral element z may be applied more than once.
element type of the resulting collection
neutral element for the operator op
the associative operator for the scan
a new iterable collection containing the prefix scan of the elements in this iterable collection
Produces a lazy list containing cumulative results of applying the operator going left to right, including the initial value.
Note: will not terminate for infinite-sized collections.
This method preserves laziness; elements are only evaluated individually as needed.
the type of the elements in the resulting collection
the initial value
the binary operator applied to the intermediate result and the element
collection with intermediate results
Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered.
Note: Even when applied to a view or a lazy collection it will always force the elements.
Example:
List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
the type of the elements in the resulting collection
the initial value
the binary operator applied to the intermediate result and the element
collection with intermediate results
Search within an interval in this sorted sequence for a specific element. If this sequence is an IndexedSeq, a binary search is used. Otherwise, a linear search is used.
The sequence should be sorted with the same Ordering before calling; otherwise, the results are undefined.
the element to find.
the index where the search starts.
the index following where the search ends.
the ordering to be used to compare elements.
a Found value containing the index corresponding to the element in the sequence, or the InsertionPoint where the element would be inserted if the element is not in the sequence.
if to <= from, the search space is empty, and an InsertionPoint at from is returned
scala.collection.SeqOps, method sorted
Search this sorted sequence for a specific element. If the sequence is an IndexedSeq, a binary search is used. Otherwise, a linear search is used.
The sequence should be sorted with the same Ordering before calling; otherwise, the results are undefined.
the element to find.
the ordering to be used to compare elements.
a Found value containing the index corresponding to the element in the sequence, or the InsertionPoint where the element would be inserted if the element is not in the sequence.
scala.collection.SeqOps, method sorted
Computes length of longest segment whose elements all satisfy some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the index where the search starts.
the length of the longest segment of this sequence starting from index from such that every element of the segment satisfies the predicate p.
Computes length of longest segment whose elements all satisfy some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the length of the longest segment of this sequence such that every element of the segment satisfies the predicate p.
The size of this sequence.
Note: will not terminate for infinite-sized collections.
the number of elements in this sequence.
Compares the size of this sequence to the size of another Iterable.
the Iterable whose size is compared with this sequence's size.
A value x where
x < 0 if this.size < that.size x == 0 if this.size == that.size x > 0 if this.size > that.size
The method as implemented here does not call size directly; its running time is O(this.size min that.size) instead of O(this.size + that.size). The method should be overridden if computing size is cheap and knownSize returns -1.
Compares the size of this sequence to a test value.
the test value that gets compared with the size.
A value x where
x < 0 if this.size < otherSize x == 0 if this.size == otherSize x > 0 if this.size > otherSize
The method as implemented here does not call size directly; its running time is O(size min otherSize) instead of O(size). The method should be overridden if computing size is cheap and knownSize returns -1.
Returns a value class containing operations for comparing the size of this iterable collection to a test value.
These operations are implemented in terms of sizeCompare(Int), and allow the following more readable usages:
this.sizeIs < size // this.sizeCompare(size) < 0 this.sizeIs <= size // this.sizeCompare(size) <= 0 this.sizeIs == size // this.sizeCompare(size) == 0 this.sizeIs != size // this.sizeCompare(size) != 0 this.sizeIs >= size // this.sizeCompare(size) >= 0 this.sizeIs > size // this.sizeCompare(size) > 0
Selects an interval of elements. The returned lazy list is made up of all elements x which satisfy the invariant:
from <= indexOf(x) < until
This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty). Additionally, it preserves laziness for all but the first from elements.
the lowest index to include from this lazy list.
the lowest index to EXCLUDE from this lazy list.
a lazy list containing the elements greater than or equal to index from extending up to (but not including) index until of this lazy list.
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
The iterator returned by this method mostly preserves laziness; size - step max 1 elements ahead of the iterator are evaluated.
the number of elements per group
the distance between the first elements of successive groups
An iterator producing lazy lists of size size, except the last element (which may be the only element) will be truncated if there are fewer than size elements remaining to be grouped.
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.) The "sliding window" step is set to one.
the number of elements per group
An iterator producing iterable collections of size size, except the last element (which may be the only element) will be truncated if there are fewer than size elements remaining to be grouped.
scala.collection.Iterator, method sliding
Sorts this sequence according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.
Note: will not terminate for infinite-sized collections.
Note: Even when applied to a view or a lazy collection it will always force the elements.
The sort is stable. That is, elements that are equal (as determined by ord.compare) appear in the same order in the sorted sequence as in the original.
the target type of the transformation f, and the type where the ordering ord is defined.
the transformation function mapping elements to some other domain B.
the ordering assumed on domain B.
a sequence consisting of the elements of this sequence sorted according to the ordering where x < y if ord.lt(f(x), f(y)).
val words = "The quick brown fox jumped over the lazy dog".split(' ')
// this works because scala.Ordering will implicitly provide an Ordering[Tuple2[Int, Char]]
words.sortBy(x => (x.length, x.head))
res0: Array[String] = Array(The, dog, fox, the, lazy, over, brown, quick, jumped)
Sorts this sequence according to a comparison function.
Note: will not terminate for infinite-sized collections.
Note: Even when applied to a view or a lazy collection it will always force the elements.
The sort is stable. That is, elements that are equal (as determined by lt) appear in the same order in the sorted sequence as in the original.
the comparison function which tests whether its first argument precedes its second argument in the desired ordering.
a sequence consisting of the elements of this sequence sorted according to the comparison function lt.
List("Steve", "Tom", "John", "Bob").sortWith(_.compareTo(_) < 0) =
List("Bob", "John", "Steve", "Tom")
Sorts this sequence according to an Ordering.
The sort is stable. That is, elements that are equal (as determined by ord.compare) appear in the same order in the sorted sequence as in the original.
the ordering to be used to compare elements.
a sequence consisting of the elements of this sequence sorted according to the ordering ord.
scala.math.Ordering Note: Even when applied to a view or a lazy collection it will always force the elements.
Splits this iterable collection into a prefix/suffix pair according to a predicate.
Note: c span p is equivalent to (but possibly more efficient than) (c takeWhile p, c dropWhile p), provided the evaluation of the predicate p does not cause any side-effects.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the test predicate
a pair consisting of the longest prefix of this iterable collection whose elements all satisfy p, and the rest of this iterable collection.
Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterators that were returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterators as well.
Splits this iterable collection into a prefix/suffix pair at a given position.
Note: c splitAt n is equivalent to (but possibly more efficient than) (c take n, c drop n).
Note: might return different results for different runs, unless the underlying collection type is ordered.
the position at which to split.
a pair of iterable collections consisting of the first n elements of this iterable collection, and the other elements.
Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterators that were returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterators as well.
Tests whether this sequence contains the given sequence at a given index.
Note: If the both the receiver object this and the argument that are infinite sequences this method may not terminate.
the sequence to test
the index where the sequence is searched.
true if the sequence that is contained in this sequence at index offset, otherwise false.
Returns a Stepper for the elements of this collection.
The Stepper enables creating a Java stream to operate on the collection, see scala.jdk.StreamConverters. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements.
The implicit StepperShape parameter defines the resulting Stepper type according to the element type of this collection.
Int, Short, Byte or Char, an IntStepper is returnedFor collections of Double or Float, a DoubleStepper is returnedFor collections of Long a LongStepper is returnedFor any other element type, an AnyStepper is returnedNote that this method is overridden in subclasses and the return type is refined to S with EfficientSplit, for example IndexedSeqOps.stepper. For Steppers marked with scala.collection.Stepper.EfficientSplit, the converters in scala.jdk.StreamConverters allow creating parallel streams, whereas bare Steppers can be converted only to sequential streams.
Sums up the elements of this collection.
the result type of the + operator.
an implicit parameter defining a set of numeric operations which includes the + operator to be used in forming the sum.
the sum of all elements of this collection with respect to the + operator in num.
The rest of the collection without its first element.
Iterates over the tails of this sequence. The first value will be this sequence and the final one will be an empty sequence, with the intervening values the results of successive applications of tail.
an iterator over all the tails of this sequence
List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)
Selects the first n elements.
This method preserves laziness; elements are only evaluated individually as needed.
the number of elements to take from this lazy list.
a lazy list consisting only of the first n elements of this lazy list, or else the whole lazy list, if it has less than n elements. If n is negative, returns an empty lazy list.
Selects the last n elements.
This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty).
the number of elements to take from this lazy list.
a lazy list consisting only of the last n elements of this lazy list, or else the whole lazy list, if it has less than n elements. If n is negative, returns an empty lazy list.
Takes longest prefix of elements that satisfy a predicate.
This method preserves laziness; elements are only evaluated individually as needed.
The predicate used to test elements.
the longest prefix of this lazy list whose elements all satisfy the predicate p.
Applies a side-effecting function to each element in this collection. Strict collections will apply f to their elements immediately, while lazy collections like Views and LazyLists will only apply f on each element if and when that element is evaluated, and each time that element is evaluated.
This method preserves laziness; elements are only evaluated individually as needed.
the return type of f
a function to apply to each element in this lazy list
The same logical collection as this
Given a collection factory factory, convert this collection to the appropriate representation for the current element type A. Example uses:
xs.to(List) xs.to(ArrayBuffer) xs.to(BitSet) // for xs: Iterable[Int]
Convert collection to array.
This collection as an Iterable[A]. No new collection will be built if this is already an Iterable[A].
This collection as a Seq[A]. This is equivalent to to(Seq) but might be faster.
This method preserves laziness; elements are only evaluated individually as needed.
a string representation of this collection. An undefined state is represented with "<not computed>" and cycles are represented with "<cycle>" Examples:
"LazyList(4, <not computed>)", a non-empty lazy list ;
"LazyList(1, 2, 3, <not computed>)", a lazy list with at least three elements ;
"LazyList(1, 2, 3, <cycle>)", an infinite lazy list that contains a cycle at the fourth element.Transposes this lazy list of iterable collections into a lazy list of lazy lists.
The resulting collection's type will be guided by the static type of lazy list. For example:
val xs = List(
Set(1, 2, 3),
Set(4, 5, 6)).transpose
// xs == List(
// List(1, 4),
// List(2, 5),
// List(3, 6))
val ys = Vector(
List(1, 2, 3),
List(4, 5, 6)).transpose
// ys == Vector(
// Vector(1, 4),
// Vector(2, 5),
// Vector(3, 6))
Note: Even when applied to a view or a lazy collection it will always force the elements.
This method evaluates all elements of the collection.
the type of the elements of each iterable collection.
an implicit conversion which asserts that the element type of this lazy list is an Iterable.
a two-dimensional lazy list of lazy lists which has as nth row the nth column of this lazy list.
Tries to extract a B from an A in a pattern matching expression.
Converts an optional function to a partial function.
Unlike Function.unlift, this UnliftOps.unlift method can be used in extractors.
val of: Int => Option[String] = { i =>
if (i == 2) {
Some("matched by an optional function")
} else {
None
}
}
util.Random.nextInt(4) match {
case of.unlift(m) => // Convert an optional function to a pattern
println(m)
case _ =>
println("Not matched")
}
Converts this lazy list of pairs into two collections of the first and second half of each pair.
val xs = `LazyList`(
(1, "one"),
(2, "two"),
(3, "three")).unzip
// xs == (`LazyList`(1, 2, 3),
// `LazyList`(one, two, three))
This method preserves laziness; elements are only evaluated individually as needed.
the type of the first half of the element pairs
the type of the second half of the element pairs
an implicit conversion which asserts that the element type of this lazy list is a pair.
a pair of lazy lists, containing the first, respectively second half of each element pair of this lazy list.
Converts this lazy list of triples into three collections of the first, second, and third element of each triple.
val xs = `LazyList`(
(1, "one", '1'),
(2, "two", '2'),
(3, "three", '3')).unzip3
// xs == (`LazyList`(1, 2, 3),
// `LazyList`(one, two, three),
// `LazyList`(1, 2, 3))
This method preserves laziness; elements are only evaluated individually as needed.
the type of the first member of the element triples
the type of the second member of the element triples
the type of the third member of the element triples
an implicit conversion which asserts that the element type of this lazy list is a triple.
a triple of lazy lists, containing the first, second, respectively third member of each element triple of this lazy list.
A copy of this lazy list with one single replaced element.
This method preserves laziness; elements are only evaluated individually as needed.
the element type of the returned lazy list.
the position of the replacement
the replacing element
a new lazy list which is a copy of this lazy list with the element at position index replaced by elem.
A view over the elements of this collection.
A collection.WithFilter which allows GC of the head of lazy list during processing.
This method is not particularly useful for a lazy list, as filter already preserves laziness.
The collection.WithFilter returned by this method preserves laziness; elements are only evaluated individually as needed.
the predicate used to test elements.
an object of class WithFilter, which supports map, flatMap, foreach, and withFilter operations. All these operations apply to those elements of this lazy list which satisfy the predicate p.
Returns a lazy list formed from this lazy list and another iterable collection by combining corresponding elements in pairs. If one of the two collections is longer than the other, its remaining elements are ignored.
This method preserves laziness; elements are only evaluated individually as needed.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
a new lazy list containing pairs consisting of corresponding elements of this lazy list and that. The length of the returned collection is the minimum of the lengths of this lazy list and that.
Returns a lazy list formed from this lazy list and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.
This method preserves laziness; elements are only evaluated individually as needed.
the iterable providing the second half of each result pair
the element to be used to fill up the result if this lazy list is shorter than that.
the element to be used to fill up the result if that is shorter than this lazy list.
a new collection of type That containing pairs consisting of corresponding elements of this lazy list and that. The length of the returned collection is the maximum of the lengths of this lazy list and that. If this lazy list is shorter than that, thisElem values are used to pad the result. If that is shorter than this lazy list, thatElem values are used to pad the result.
Zips this lazy list with its indices.
This method preserves laziness; elements are only evaluated individually as needed.
A new lazy list containing pairs consisting of all elements of this lazy list paired with their index. Indices start at 0.
© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/collection/immutable/LazyList.html
This class implements an immutable linked list that evaluates elements in order and only when needed. Here is an example:
import scala.math.BigInt object Main extends App { val fibs: LazyList[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip(fibs.tail).map { n => n._1 + n._2 } fibs take 5 foreach println } // prints // // 0 // 1 // 1 // 2 // 3Elements of a
LazyListare memoized; that is, the value of each element is computed only once. To illustrate, we will alter body of thefibsvalue above and take some more values:import scala.math.BigInt object Main extends App { val fibs: LazyList[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip( fibs.tail).map(n => { println("Adding %d and %d".format(n._1, n._2)) n._1 + n._2 }) fibs take 5 foreach println fibs take 6 foreach println } // prints // // 0 // 1 // Adding 0 and 1 // 1 // Adding 1 and 1 // 2 // Adding 1 and 2 // 3 // And then prints // // 0 // 1 // 1 // 2 // 3 // Adding 2 and 3 // 5There are a number of subtle points to the above example.
fibsis avalnot a method. The memoization of theLazyListrequires us to have somewhere to store the information and avalallows us to do that.LazyListis actually being modified during access, this does not change the notion of its immutability. Once the values are memoized they do not change and values that have yet to be memoized still "exist", they simply haven't been realized yet.LazyListcreates a structure much like scala.collection.immutable.List. So long as something is holding on to the head, the head holds on to the tail, and so it continues recursively. If, on the other hand, there is nothing holding on to the head (e.g. we useddefto define theLazyList) then once it is no longer being used directly, it disappears.LazyList, and a lazy list holds its own head. For computations of this sort where memoization is not desired, useIteratorwhen possible.// For example, let's build the natural numbers and do some silly iteration // over them. // We'll start with a silly iteration def loop(s: String, i: Int, iter: Iterator[Int]): Unit = { // Stop after 200,000 if (i < 200001) { if (i % 50000 == 0) println(s + i) loop(s, iter.next(), iter) } } // Our first LazyList definition will be a val definition val lazylist1: LazyList[Int] = { def loop(v: Int): LazyList[Int] = v #:: loop(v + 1) loop(0) } // Because lazylist1 is a val, everything that the iterator produces is held // by virtue of the fact that the head of the LazyList is held in lazylist1 val it1 = lazylist1.iterator loop("Iterator1: ", it1.next(), it1) // We can redefine this LazyList such that all we have is the Iterator left // and allow the LazyList to be garbage collected as required. Using a def // to provide the LazyList ensures that no val is holding onto the head as // is the case with lazylist1 def lazylist2: LazyList[Int] = { def loop(v: Int): LazyList[Int] = v #:: loop(v + 1) loop(0) } val it2 = lazylist2.iterator loop("Iterator2: ", it2.next(), it2) // And, of course, we don't actually need a LazyList at all for such a simple // problem. There's no reason to use a LazyList if you don't actually need // one. val it3 = new Iterator[Int] { var i = -1 def hasNext = true def next(): Int = { i += 1; i } } loop("Iterator3: ", it3.next(), it3)tailworks at all is of interest. In the definition offibswe have an initial(0, 1, LazyList(...))sotailis deterministic. If we definedfibssuch that only0were concretely known then the act of determiningtailwould require the evaluation oftailwhich would cause an infinite recursion and stack overflow. If we define a definition where the tail is not initially computable then we're going to have an infinite recursion:// The first time we try to access the tail we're going to need more // information which will require us to recurse, which will require us to // recurse, which... lazy val sov: LazyList[Vector[Int]] = Vector(0) #:: sov.zip(sov.tail).map { n => n._1 ++ n._2 }The definition of
fibsabove creates a larger number of objects than necessary depending on how you might want to implement it. The following implementation provides a more "cost effective" implementation due to the fact that it has a more direct route to the numbers themselves:lazy val fib: LazyList[Int] = { def loop(h: Int, n: Int): LazyList[Int] = h #:: loop(n, h + n) loop(1, 1) }the type of the elements contained in this lazy list.
2.13
"Scala's Collection Library overview" section on
LazyListsfor more information.