How to use ismember in a cell array?

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'."

Answer 1

[Jan]

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.

[Jan]

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.

Answer 2

[Stephen23]

>> 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

[Dominik Mattioli]

This is what I expected, however Jan's right about the loops. For my code, a loop was faster. Must be the overhead of cellfun. Thanks though!

[Emmanuel Lasso]

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