How to do element by element comparison?

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Given a 2d matrix, say 10x4 with many numbers, lots of which are zeros, I need a matrix that replaces every zero entry with the value of the last non-zero entry in the same column that is before it. for example for the given input:
[0 0 4 0;
0 3 1 0;
0 0 0 2;
0 0 6 2;
3 4 5 6;
8 0 0 9;
0 0 0 0;
0 0 0 0;
0 0 0 0]
output:
[0 0 4 0;
0 3 1 0;
0 3 1 2;
0 3 6 2;
3 4 5 6;
8 4 5 9;
8 4 5 9;
8 4 5 9;
8 4 5 9]
I've experimented with circshift, if statements and for loops but haven't been able to make much headway. Does anyone have suggestions?

Accepted Answer

venkat vasu
venkat vasu on 17 Oct 2012
Edited: Matt Fig on 17 Oct 2012
Hi.. This code surely will help you and you can check n matrix also.
a=[0 0 4 0; 0 3 1 0; 0 0 0 2; 0 0 6 2; 3 4 5 6; 8 0 0 9; 0 0 0 0; 0 0 0 0; 0 0 0 0];
[r c d]=size(a);
for i=1:r
j=a(i,:);
if i==1
prev=j;
else
b=find(j==0);
for k=1:length(b);
a(i,b(k))=prev(b(k));
end
prev=a(i,:);
end
end
a

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