# Extract non zero elements from 2D array

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Tha saliem on 2 Apr 2017
Commented: Stephen23 on 2 Apr 2017
Hi I have an array like this:
I want to extract non-zero elements for each row, e.g for second row, it should be 3,4. (and other array elements are zero) for third row 1,3,4 I think 3d array will be used and i tried this code, but incorrect results.
for m=1:r
for k=1:row
for l=1:col
if(a(k,l)~=0)
b(k,l,m)=a(k,l);
end
end
end
end
(a for array given above and b is new array with results) Any help will be highly appreciated.

Stephen23 on 2 Apr 2017
No ugly loops are required:
>> [R,C] = find(X)
>> out = accumarray(R,X(X~=0),[],@(n){n});
>> out{2} % second row
ans =
4
3
>> out{3} % third row
ans =
3
1
4
Stephen23 on 2 Apr 2017
@Tha saliem: sure, anything is possible, but you need to tell us what you want to do with the unequally-sized vectors. Do you want to pad them to the same size, or what?
For example, exactly how do you want [3;4] and [1;3;4] arranged in this 3D array, considering that they have different lengths?

Nicolaie Popescu-Bodorin on 2 Apr 2017
Edited: Stephen23 on 2 Apr 2017
% Let A be a 2D Array and NZI the cell containing indices of non-zero elements on each column.
% preallocation:
sa = size(A,2); NZI{sa}=[];
for k=1:sa,
NZI{k} = find(A(:,k)~=0);
end
Kind regards, Nicolaie Popescu-Bodorin, www.lmrec.org/bodorin/
Tha saliem on 2 Apr 2017
Thanks alot.