Find the indices of elements of a cell array whose length is 1.

I have a cell array say, B{1}=[1,2], B{2}=[2], B{3}=3. I want to find the indices which give elements of length 1. In this case I want 2,3 as answers because B{2},B{3} have only single elements.

Answer 1

[the cyclist]

find(cellfun(@isscalar,B))

cellfun applies a function to each element of a cell. You can do more complicated things, but it just so happens that there was also a function, isscalar, that does the "test" that you want.

Answer 2

[Kirby Fears]

You can apply an operation to each cell using cellfun(). Below is sample code that checks if each cell contains one element. The output is a logical array the same size as B. You can use find() on this logical array to get the position indices.

B{1} = [1,2];
B{2} = 2;
B{3} = 3;
idxSingles = find(cellfun(@(c) numel(c)==1 ,B));

Hope this helps.

[ashok Vardhan]

How can I declare such a cell-array in Matlab where size of each sub-array is not equal ? I mean how do I create such an array.

[Kirby Fears]

You initialize the cell array by using the cell() function. Then assign the double arrays into each cell.

 B=cell(3,1); % initializes 3x1 cell array
 B{1} = [1,2,3]; % 1st cell is 1x3 double array
 B{2} = [4,5,6,7,8]; % 2nd cell is 1x5 double array
 B{3} = [9,10]; % 3rd cell is 1x2 double array

If you are reading lots of data from somewhere, you should populate the cell array programmatically. The way to do this depends on what your data looks like and how you are reading it into Matlab.

Hope this helps.