6.3.3 Indexing Cell Arrays

As shown in see Basic Usage of Cell Arrays elements can be extracted from cell arrays using the ‘{’ and ‘}’ operators. If you want to extract or access subarrays which are still cell arrays, you need to use the ‘(’ and ‘)’ operators. The following example illustrates the difference:

c = {"1", "2", "3"; "x", "y", "z"; "4", "5", "6"};
c{2,3}
     ⇒ ans = z

c(2,3)
     ⇒ ans =
        {
          [1,1] = z
        }

So with ‘{}’ you access elements of a cell array, while with ‘()’ you access a sub array of a cell array.

Using the ‘(’ and ‘)’ operators, indexing works for cell arrays like for multi-dimensional arrays. As an example, all the rows of the first and third column of a cell array can be set to 0 with the following command:

c(:, [1, 3]) = {0}
     ⇒ =
        {
          [1,1] = 0
          [2,1] = 0
          [3,1] = 0
          [1,2] = 2
          [2,2] = y
          [3,2] = 5
          [1,3] = 0
          [2,3] = 0
          [3,3] = 0
        }

Note, that the above can also be achieved like this:

c(:, [1, 3]) = 0;

Here, the scalar ‘0’ is automatically promoted to cell array ‘{0}’ and then assigned to the subarray of c.

To give another example for indexing cell arrays with ‘()’, you can exchange the first and the second row of a cell array as in the following command:

c = {1, 2, 3; 4, 5, 6};
c([1, 2], :) = c([2, 1], :)
     ⇒ =
        {
          [1,1] =  4
          [2,1] =  1
          [1,2] =  5
          [2,2] =  2
          [1,3] =  6
          [2,3] =  3
        }

Accessing multiple elements of a cell array with the ‘{’ and ‘}’ operators will result in a comma-separated list of all the requested elements (see Comma Separated Lists). Using the ‘{’ and ‘}’ operators the first two rows in the above example can be swapped back like this:

[c{[1,2], :}] = deal (c{[2, 1], :})
     ⇒ =
        {
          [1,1] =  1
          [2,1] =  4
          [1,2] =  2
          [2,2] =  5
          [1,3] =  3
          [2,3] =  6
        }

As for struct arrays and numerical arrays, the empty matrix ‘[]’ can be used to delete elements from a cell array:

x = {"1", "2"; "3", "4"};
x(1, :) = []
     ⇒ x =
        {
          [1,1] = 3
          [1,2] = 4
        }

The following example shows how to just remove the contents of cell array elements but not delete the space for them:

x = {"1", "2"; "3", "4"};
x(1, :) = {[]}
⇒ x =
      {
        [1,1] = [](0x0)
        [2,1] = 3
        [1,2] = [](0x0)
        [2,2] = 4
      }

The indexing operations operate on the cell array and not on the objects within the cell array. By contrast, cellindexmat applies matrix indexing to the objects within each cell array entry and returns the requested values.

y = cellindexmat (x, varargin)

Perform indexing of matrices in a cell array.

Given a cell array of matrices x, this function computes

Y = cell (size (X));
for i = 1:numel (X)
  Y{i} = X{i}(varargin{1}, varargin{2}, …, varargin{N});
endfor

The indexing arguments may be scalar (2), arrays ([1, 3]), ranges (1:3), or the colon operator (":"). However, the indexing keyword end is not available.

See also: cellslices, cellfun.