6.2.3 Indexing Cell Arrays

As shown in see section 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"; "a", "b", "c"; "4", "5", "6"};
c{2,3}
     ⇒ ans = c

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

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 multidimensional 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] =  10
          [3,2] =  20
          [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 section 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
      }