在MATLAB中从单元格数组中删除元素

Question

I have a cell array as shown below:

a = {[1 2 3] [5 3 6] [9 1 3]};

Now I want to remove the 1s from every array in a that contains 1 so that the output is as shown

a = {[2 3] [5 3 6] [9 3]};

I know the indices of arrays in cell array 'a' which contain 1. This can be done using for loop and a temporary variable, but this is taking a lot of time (I want to perform the operation on a cell array of size something like 1x100000. The one above is just for an example)

I want to know if there is any direct method that can do this quickly.

Answer 1

Pretty much anything is going to be slow with that large of a cell array. You could try to do this with cellfun but it's not necessarily guaranteed to be any faster than a for loop.

a = cellfun(@(x)x(x ~= 1), a, 'UniformOutput', false);

%   a{1} =
%        2     3
%   a{2} =
%        5     3     6
%   a{3} =
%        9     3

Answer 2

As already commented by Suever, because you are using a cell array and it is a dynamic container, you don't have a choice but to iterate through each cell if you want to modify the contents. Just to be self-contained, here is the for loop approach to do things:

for ii = 1 : numel(a)
    a{ii} = a{ii}(a{ii} ~= 1);
end

This may be faster as it doesn't undergo the overhead of cellfun . The code above accesses the vector in each cell and extracts out those values that are not equal to 1 and overwrites the corresponding cell with this new vector.

Using your example:

a = {[1 2 3] [5 3 6] [9 1 3]};

We get:

>> format compact; celldisp(a)
a{1} =
     2     3
a{2} =
     5     3     6
a{3} =
     9     3

Answer 3

This example shows how to remove data from individual cells, and how to delete entire cells from a cell array. To run the code in this example, create a 3-by-3 cell array:

C = {1, 2, 3; 4, 5, 6; 7, 8, 9};

Delete the contents of a particular cell by assigning an empty array to the cell, using curly braces for content indexing, {}:

C{2,2} = []

This code returns

C = 
    [1]    [2]    [3]
    [4]     []    [6]
    [7]    [8]    [9]

Delete sets of cells using standard array indexing with smooth parentheses, (). For example, this command

C(2,:) = []

removes the second row of C:

`

C = 
    [1]    [2]    [3]
    [7]    [8]    [9]`