How to compare rows in a matrix

Hello all

I have a matrix A

A =

       1     1     0     0     0
       0    -1     0     1     0
      -1     0     1     1     0

lets say I am looking at the second row in which column 2 and 4 have value present now if I compare it with the row above which has values in the column 1 and column 2 so I want to know the column number which has values in both the rows, I mean here the column number 2 should be returned. Similarly row 3 should be compared with row 1 and 2 and for each row a column number should be returned.

Can anyone please guide me through this.

Regards

[Azzi Abdelmalek]

What is the expected result for your example?

Answer 1

[Azzi Abdelmalek]

Comparison between row 1 and row 2

A =[ 1     1     0     0     0
     0    -1     0     1     0
    -1     0     1     1     0]
idx=find(all(A(1:2,:)))

[Sameer]

Hi thanks for replying. The answer for second row must be 2 which is correct as per the suggested approach but for the third row answer should be 1 and 4 as when we consider 3 row then it should be compared to 1st row and gives me 1 and then with second row andgive me 4 so theanswer for 3rd row should be 1 and 4.

Regards

[Azzi Abdelmalek]

A =[ 1     1     0     0     0
     0    -1     0     1     0
    -1     0     1     1     0]
jj=0;
for k=2:size(A,1)
   for p=1:k-1
       B=A([p,k],:)
       jj=jj+1;
      out{jj,2}=find(all(B))
      out{jj,1}=sprintf('(%d,%d)',k,p)
   end
end

[Sameer]

Thanks a lot

Answer 2

[the cyclist]

I think that

[rows,cols] = find(A(2:end,:)~=0 & A(1:end-1,:)~=0)

does what you want.

rows will be the index to the "top" row being compared, and "cols" will be the column numbers that meet your criterion.

For example, in your case

rows = [1; 2];

and

cols = [2; 4];

cols seems to be the main thing you are going for.

[the cyclist]

My solution only compares neighboring pairs of rows.

[Sameer]

Thanks a lot