CODEWITHSUNDEEP
matlaboctave
user220878
user220878

Reputation:

Finding all rows in a pair of vectors where both entries are non-zero (Octave)

I have a n x 2 matrix in Octave, and I would like to find every row where the matrix(row, 1) and matrix(row, 2) elements are non-zero. I could use a for loop like this:

[nrows, ncols] = size(data);
for i = 1:nrows
    if(data(i, 1) ~= 0 && data(i, 2) ~= 0)
        % Do something
    end
end

The issue with that is that n is about 3 million, and iteration in Octave takes for ever. I feel like there is a way to do it with find, but I haven't been able to figure it out yet.

Anyone have any advice?

Thanks!

Upvotes: 0

Views: 198

Answers (3)

Dedek Mraz
Dedek Mraz

Reputation: 814

If performance is the issue: maybe try converting both columns to logical:

useful = and(logical(data(:,1)),logical(data(:,2)))

Then you can again use logical indexing:

filtered = data(useful,:)

Upvotes: 0

ZZZ
ZZZ

Reputation: 724

I think in this case (since it is related with zero values) the following also should work

idx=(data(:,1).*data(:,2)~=0)

But @H.Muster's solution is the one that works in all cases, hence a better one.

Upvotes: 0

H.Muster
H.Muster

Reputation: 9317

You can create use logical indexing:

idx = all(data(:,1:2)~=0, 2);

The resulting vector idx contains 1s in every row where both cells are non-zero and 0 otherwise.

Upvotes: 2

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