# How to use ismember in a cell array?

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Dominik Mattioli on 21 Feb 2017
Edited: Emmanuel Lasso on 6 Oct 2019
I would like to change the value of some value within a cell array that has only numeric data, preferably not using loops because I will be performing this operation with large cell arrays many times.
% Given:
A = {[1 2 3] [3 4 5 6];[7 8] [9 1 2 3 4];[5] [6 7 8 9]};
B = 1;
% Set all values in A equal to B as NaN.
% If A were a double then it would look like this:
A(ismember(A,B)) = NaN;
I've been trying to use this
A(cellfun(@(x) x == B(1),A,'un',0))
But I get this error:
"Function 'subsindex' is not defined for values of class 'cell'."

Jan on 21 Feb 2017
Try it with loops, because there is no general rule that loops are slow:
A = {[1 2 3] [3 4 5 6];[7 8] [9 1 2 3 4];[5] [6 7 8 9]};
B = 1;
for iA = 1:numel(A)
tmpA = A{iA};
tmpA(tmpA == B) = NaN;
A{iA} = tmpA;
end
Measure the timings using timeit or tic/toc. cellfun with anonymous function is not really fast also, because handling the anonymos function for each element needs some time, perhaps more than the loop overhead.
##### 1 CommentShowHide None
Jan on 21 Feb 2017
Note that strrep is very efficient with replacing characters in cell strings. Unfortunately this command does not accept numerical values as e.g. strfind does. But a C-Mex might be much faster, so consider to mex this, if it is the bottleneck of your code.

### More Answers (1)

Stephen23 on 21 Feb 2017
Edited: Stephen23 on 21 Feb 2017
>> A = {[1,2,3],[3,4,5,6];[7,8],[9,1,2,3,4];[5],[6,7,8,9]};
>> B = 1;
>> C = cellfun(@(a)a~=B,A,'Uni',0);
>> D = cellfun(@(a,c)a.*(c./c),A,C,'Uni',0);
>> D{:}
ans =
NaN 2 3
ans =
7 8
ans = 5
ans =
3 4 5 6
ans =
9 NaN 2 3 4
ans =
6 7 8 9
##### 2 CommentsShowHide 1 older comment
Emmanuel Lasso on 6 Oct 2019
Edited: Emmanuel Lasso on 6 Oct 2019
And if I want to replace a value of an array, i mean, in this case B = [3 2 1 0], and C should find the values that match from A, A variates between 3 and 0 like randi function, so how D can use cellfun for search in A the values that match and replace with another values?. For example if a~=3 then replace it with -3