How to do element by element comparison?

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?

[Rob]

Brilliant!! Thank you!!

Answer 1

[venkat vasu]

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

[Azzi Abdelmalek]

Format your answer http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup