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How to compare rows in a matrix

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Sameer
Sameer on 18 Jul 2014
Commented: Sameer on 18 Jul 2014
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

  1 Comment

Azzi Abdelmalek
Azzi Abdelmalek on 18 Jul 2014
What is the expected result for your example?

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Accepted Answer

Azzi Abdelmalek
Azzi Abdelmalek on 18 Jul 2014
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,:)))

  3 Comments

Sameer
Sameer on 18 Jul 2014
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
Azzi Abdelmalek on 18 Jul 2014
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

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More Answers (1)

the cyclist
the cyclist on 18 Jul 2014
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.

  2 Comments

the cyclist
the cyclist on 18 Jul 2014
My solution only compares neighboring pairs of rows.

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