MATLAB: Indices to zeros in Matrix

find

Suppose:
A =
       4     5     1     3
       5     1     3     4
       5     0     0     0
       6     0     0     0
       4     0     0     0
       4     0     0     0
       3     0     0     0
I want to find the indices to the rows that contain 0 and I used:
[r,c]=find(A==0)
However, r returned
3
4
5
6
7
3
4
5
6
7
3
4
5
6
7
Why is this so? Shouldn't it return 3,4,5,6,7 only?

Best Answer

[r,c] = find(A == 0) returns in r and c the row and column indices of every single zero in the array. Therefore, you're going to get multiples like that. If you want to find which rows contain zeros rather than where each zero is located, you could do one of the following:
r = find(any(~A,2));
Or:
[r,c] = find(A == 0);
r = unique(r);
The first option is preferable, as it is much faster.
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