This module implements operations for the built-in seq type which were inspired by functional programming languages.
For functional style programming you may want to pass anonymous procs to procs like filter
to reduce typing. Anonymous procs can use the special do notation which is more convenient in certain situations.
proc concat[T](seqs: varargs[seq[T]]): seq[T]
Takes several sequences' items and returns them inside a new sequence.
Example:
let s1 = @[1, 2, 3] s2 = @[4, 5] s3 = @[6, 7] total = concat(s1, s2, s3) assert total == @[1, 2, 3, 4, 5, 6, 7]
proc cycle[T](s: seq[T]; n: Natural): seq[T]
Returns a new sequence with the items of s repeated n times.
Example:
- let
- s = @[1, 2, 3] total = s.cycle(3)
assert total == @[1, 2, 3, 1, 2, 3, 1, 2, 3]
proc repeat[T](x: T; n: Natural): seq[T]
Returns a new sequence with the item x repeated n times.
Example:
- let
- total = repeat(5, 3)
assert total == @[5, 5, 5]
proc deduplicate[T](seq1: seq[T]): seq[T]
let dup1 = @[1, 1, 3, 4, 2, 2, 8, 1, 4] dup2 = @["a", "a", "c", "d", "d"] unique1 = deduplicate(dup1) unique2 = deduplicate(dup2) assert unique1 == @[1, 3, 4, 2, 8] assert unique2 == @["a", "c", "d"]
proc zip[S, T](seq1: seq[S]; seq2: seq[T]): seq[tuple[a: S, b: T]]
Returns a new sequence with a combination of the two input sequences.
For convenience you can access the returned tuples through the named fields a and b. If one sequence is shorter, the remaining items in the longer sequence are discarded. Example:
let short = @[1, 2, 3] long = @[6, 5, 4, 3, 2, 1] words = @["one", "two", "three"] zip1 = zip(short, long) zip2 = zip(short, words) assert zip1 == @[(1, 6), (2, 5), (3, 4)] assert zip2 == @[(1, "one"), (2, "two"), (3, "three")] assert zip1[2].b == 4 assert zip2[2].b == "three"
proc distribute[T](s: seq[T]; num: Positive; spread = true): seq[seq[T]]
Splits and distributes a sequence s into num sub sequences.
Returns a sequence of num sequences. For some input values this is the inverse of the concat proc. The proc will assert in debug builds if s is nil or num is less than one, and will likely crash on release builds. The input sequence s can be empty, which will produce num empty sequences.
If spread is false and the length of s is not a multiple of num, the proc will max out the first sub sequences with 1 + len(s) div num
entries, leaving the remainder of elements to the last sequence.
On the other hand, if spread is true, the proc will distribute evenly the remainder of the division across all sequences, which makes the result more suited to multithreading where you are passing equal sized work units to a thread pool and want to maximize core usage.
Example:
let numbers = @[1, 2, 3, 4, 5, 6, 7] assert numbers.distribute(3) == @[@[1, 2, 3], @[4, 5], @[6, 7]] assert numbers.distribute(3, false) == @[@[1, 2, 3], @[4, 5, 6], @[7]] assert numbers.distribute(6)[0] == @[1, 2] assert numbers.distribute(6)[5] == @[7]
proc map[T, S](data: openArray[T]; op: proc (x: T): S {.closure.}): seq[S] {.inline.}
Returns a new sequence with the results of op applied to every item in data.
Since the input is not modified you can use this version of map
to transform the type of the elements in the input sequence. Example:
let a = @[1, 2, 3, 4] b = map(a, proc(x: int): string = $x) assert b == @["1", "2", "3", "4"]
proc map[T](data: var openArray[T]; op: proc (x: var T) {.closure.}) {.deprecated.}
Applies op to every item in data modifying it directly.
Note that this version of map
requires your input and output types to be the same, since they are modified in-place. Example:
var a = @["1", "2", "3", "4"] echo repr(a) # --> ["1", "2", "3", "4"] map(a, proc(x: var string) = x &= "42") echo repr(a) # --> ["142", "242", "342", "442"]
Deprecated since version 0.12.0: Use the apply
proc instead.
proc apply[T](data: var seq[T]; op: proc (x: var T) {.closure.}) {.inline.}
Applies op to every item in data modifying it directly.
Note that this requires your input and output types to be the same, since they are modified in-place. The parameter function takes a var T
type parameter. Example:
var a = @["1", "2", "3", "4"] echo repr(a) # --> ["1", "2", "3", "4"] apply(a, proc(x: var string) = x &= "42") echo repr(a) # --> ["142", "242", "342", "442"]
proc apply[T](data: var seq[T]; op: proc (x: T): T {.closure.}) {.inline.}
Applies op to every item in data modifying it directly.
Note that this requires your input and output types to be the same, since they are modified in-place. The parameter function takes and returns a T
type variable. Example:
var a = @["1", "2", "3", "4"] echo repr(a) # --> ["1", "2", "3", "4"] apply(a, proc(x: string): string = x & "42") echo repr(a) # --> ["142", "242", "342", "442"]
proc filter[T](seq1: seq[T]; pred: proc (item: T): bool {.closure.}): seq[T] {.inline.}
Returns a new sequence with all the items that fulfilled the predicate.
Example:
let colors = @["red", "yellow", "black"] f1 = filter(colors, proc(x: string): bool = x.len < 6) f2 = filter(colors) do (x: string) -> bool : x.len > 5 assert f1 == @["red", "black"] assert f2 == @["yellow"]
proc keepIf[T](seq1: var seq[T]; pred: proc (item: T): bool {.closure.}) {.inline.}
Keeps the items in the passed sequence if they fulfilled the predicate. Same as the filter
proc, but modifies the sequence directly.
Example:
var floats = @[13.0, 12.5, 5.8, 2.0, 6.1, 9.9, 10.1] keepIf(floats, proc(x: float): bool = x > 10) assert floats == @[13.0, 12.5, 10.1]
proc delete[T](s: var seq[T]; first, last: Natural)
Deletes in s the items at position first .. last. This modifies s itself, it does not return a copy.
Example:
let outcome = @[1,1,1,1,1,1,1,1] var dest = @[1,1,1,2,2,2,2,2,2,1,1,1,1,1] dest.delete(3, 8) assert outcome == dest
proc insert[T](dest: var seq[T]; src: openArray[T]; pos = 0)
Inserts items from src into dest at position pos. This modifies dest itself, it does not return a copy.
Example:
var dest = @[1,1,1,1,1,1,1,1] let src = @[2,2,2,2,2,2] outcome = @[1,1,1,2,2,2,2,2,2,1,1,1,1,1] dest.insert(src, 3) assert dest == outcome
proc all[T](seq1: seq[T]; pred: proc (item: T): bool {.closure.}): bool
Iterates through a sequence and checks if every item fulfills the predicate.
Example:
let numbers = @[1, 4, 5, 8, 9, 7, 4] assert all(numbers, proc (x: int): bool = return x < 10) == true assert all(numbers, proc (x: int): bool = return x < 9) == false
proc any[T](seq1: seq[T]; pred: proc (item: T): bool {.closure.}): bool
Iterates through a sequence and checks if some item fulfills the predicate.
Example:
let numbers = @[1, 4, 5, 8, 9, 7, 4] assert any(numbers, proc (x: int): bool = return x > 8) == true assert any(numbers, proc (x: int): bool = return x > 9) == false
iterator filter[T](seq1: seq[T]; pred: proc (item: T): bool {.closure.}): T
Iterates through a sequence and yields every item that fulfills the predicate.
Example:
let numbers = @[1, 4, 5, 8, 9, 7, 4] for n in filter(numbers, proc (x: int): bool = x mod 2 == 0): echo($n) # echoes 4, 8, 4 in separate lines
template filterIt(seq1, pred: untyped): untyped
Returns a new sequence with all the items that fulfilled the predicate.
Unlike the proc version, the predicate needs to be an expression using the it
variable for testing, like: filterIt("abcxyz", it == 'x')
. Example:
let temperatures = @[-272.15, -2.0, 24.5, 44.31, 99.9, -113.44] acceptable = filterIt(temperatures, it < 50 and it > -10) notAcceptable = filterIt(temperatures, it > 50 or it < -10) assert acceptable == @[-2.0, 24.5, 44.31] assert notAcceptable == @[-272.15, 99.9, -113.44]
template keepItIf(varSeq: seq; pred: untyped)
Convenience template around the keepIf
proc to reduce typing.
Unlike the proc version, the predicate needs to be an expression using the it
variable for testing, like: keepItIf("abcxyz", it == 'x')
. Example:
var candidates = @["foo", "bar", "baz", "foobar"] keepItIf(candidates, it.len == 3 and it[0] == 'b') assert candidates == @["bar", "baz"]
template allIt(seq1, pred: untyped): bool
Checks if every item fulfills the predicate.
Example:
let numbers = @[1, 4, 5, 8, 9, 7, 4] assert allIt(numbers, it < 10) == true assert allIt(numbers, it < 9) == false
template anyIt(seq1, pred: untyped): bool
Checks if some item fulfills the predicate.
Example:
let numbers = @[1, 4, 5, 8, 9, 7, 4] assert anyIt(numbers, it > 8) == true assert anyIt(numbers, it > 9) == false
template toSeq(iter: untyped): untyped
Transforms any iterator into a sequence.
Example:
let numeric = @[1, 2, 3, 4, 5, 6, 7, 8, 9] odd_numbers = toSeq(filter(numeric) do (x: int) -> bool: if x mod 2 == 1: result = true) assert odd_numbers == @[1, 3, 5, 7, 9]
template foldl(sequence, operation: untyped): untyped
Template to fold a sequence from left to right, returning the accumulation.
The sequence is required to have at least a single element. Debug versions of your program will assert in this situation but release versions will happily go ahead. If the sequence has a single element it will be returned without applying operation
.
The operation
parameter should be an expression which uses the variables a
and b
for each step of the fold. Since this is a left fold, for non associative binary operations like subtraction think that the sequence of numbers 1, 2 and 3 will be parenthesized as (((1) - 2) - 3). Example:
let numbers = @[5, 9, 11] addition = foldl(numbers, a + b) subtraction = foldl(numbers, a - b) multiplication = foldl(numbers, a * b) words = @["nim", "is", "cool"] concatenation = foldl(words, a & b) assert addition == 25, "Addition is (((5)+9)+11)" assert subtraction == -15, "Subtraction is (((5)-9)-11)" assert multiplication == 495, "Multiplication is (((5)*9)*11)" assert concatenation == "nimiscool"
template foldl(sequence, operation, first): untyped
Template to fold a sequence from left to right, returning the accumulation.
This version of foldl
gets a starting parameter. This makes it possible to accumulate the sequence into a different type than the sequence elements.
The operation
parameter should be an expression which uses the variables a
and b
for each step of the fold. The first
parameter is the start value (the first a
) and therefor defines the type of the result. Example:
let numbers = @[0, 8, 1, 5] digits = foldl(numbers, a & (chr(b + ord('0'))), "") assert digits == "0815"
template foldr(sequence, operation: untyped): untyped
Template to fold a sequence from right to left, returning the accumulation.
The sequence is required to have at least a single element. Debug versions of your program will assert in this situation but release versions will happily go ahead. If the sequence has a single element it will be returned without applying operation
.
The operation
parameter should be an expression which uses the variables a
and b
for each step of the fold. Since this is a right fold, for non associative binary operations like subtraction think that the sequence of numbers 1, 2 and 3 will be parenthesized as (1 - (2 - (3))). Example:
let numbers = @[5, 9, 11] addition = foldr(numbers, a + b) subtraction = foldr(numbers, a - b) multiplication = foldr(numbers, a * b) words = @["nim", "is", "cool"] concatenation = foldr(words, a & b) assert addition == 25, "Addition is (5+(9+(11)))" assert subtraction == 7, "Subtraction is (5-(9-(11)))" assert multiplication == 495, "Multiplication is (5*(9*(11)))" assert concatenation == "nimiscool"
template mapIt(seq1, typ, op: untyped): untyped
Convenience template around the map
proc to reduce typing.
The template injects the it
variable which you can use directly in an expression. You also need to pass as typ the type of the expression, since the new returned sequence can have a different type than the original. Example:
let nums = @[1, 2, 3, 4] strings = nums.mapIt(string, $(4 * it)) assert strings == @["4", "8", "12", "16"]
mapIt(seq1, op)
template mapIt(seq1, op: untyped): untyped
Convenience template around the map
proc to reduce typing.
The template injects the it
variable which you can use directly in an expression. Example:
let nums = @[1, 2, 3, 4] strings = nums.mapIt($(4 * it)) assert strings == @["4", "8", "12", "16"]
template applyIt(varSeq, op: untyped)
Convenience template around the mutable apply
proc to reduce typing.
The template injects the it
variable which you can use directly in an expression. The expression has to return the same type as the sequence you are mutating. Example:
var nums = @[1, 2, 3, 4] nums.applyIt(it * 3) assert nums[0] + nums[3] == 15
template newSeqWith(len: int; init: untyped): untyped
var seq2D = newSeqWith(20, newSeq[bool](10)) seq2D[0][0] = true seq2D[1][0] = true seq2D[0][1] = true import random var seqRand = newSeqWith(20, random(10)) echo seqRand
© 2006–2017 Andreas Rumpf
Licensed under the MIT License.
https://nim-lang.org/docs/sequtils.html