MATLAB Answers

## Mapping a function over each cell in a cell array using arrayfun

Asked by Andrew

### Andrew (view profile)

on 10 May 2011
Accepted Answer by Walter Roberson

### Walter Roberson (view profile)

Hi,
I am trying to "map" a function over each cell in a cell array. For example, suppose that I have a cell array which is filled with vectors of the same length:
C=cell(2,2);
C(1,1)={[1,1]};
C(1,2)={[2,2]};
C(2,1)={[3,3]};
C(2,2)={[4,4]};
Now I wish to apply the built-in Matlab function "norm" to each element in the cell array and return the results in an array (a regular, numeric array/matrix). I tried the following:
myresult=arrayfun(@(M,N) norm(cell2mat(C(M,N))),1:size(C,1),1:size(C,2))
But of course this does not give me what I really want; it gives me the following:
myresult =
1.4142 5.6569
which is only the norm of the (1,1) element (note that sqrt(1.^2 + 1.^2) = 1.4142) and the norm of the (2,2) element (note that sqrt(4.^2 + 4.^2) = 5.6569). This is because in my code, by specifying M as 1:size(C,1) and N as 1:size(C,2), the function is only evaluated at (M,N)=(1,1) and (M,N)=(2,2).
Can you please help me to see how I can modify my code to take the norm of all the arrays stored in the cell array C?
Thanks in advance,
Andrew DeYoung
Carnegie Mellon University

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## 1 Answer ### Walter Roberson (view profile)

Answer by Walter Roberson

### Walter Roberson (view profile)

on 10 May 2011
Accepted Answer

myresult = arrayfun(@(c) norm(c{1}), C);
Or more compactly,
myresult = cellfun(@norm,C);

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