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matlabmatrixrowsextract
henry
henry

Reputation: 965

Find rows that contain only zeros

I have a huge matrix in MATLAB. Now some rows contain only zeros.

Can I use the function find to find all the rows which contain only zeros ?

Upvotes: 2

Views: 3783

Answers (3)

Charu Sharma
Charu Sharma

Reputation: 1

n = length(matrix);

This line will give you the number of rows in a matrix.

ids = setdiff(1:n,find(sum(matrix,2)));

ids will give you the row numbers(indexes) which contain only zeros.

Upvotes: 0

S Geurts
S Geurts

Reputation: 118

If you need, you can obtain more speed (depending on your dataset) by first looking for partial zero rows (in this example length 10) and computing further with the selection of rows.

row_has_first10_zeros = sum(data(:,1:10),2);
row_has_all_zeros = sum(data(~rows,:),2);

indices = find(~row_has_first10_zeros)
indices = indices(~row_has_all_zeros)

Upvotes: 0

Suever
Suever

Reputation: 65430

You can use any to find any rows that have non-zeros and then negate the result. We use the second input to specify that we want to apply the operation across the columns (the 2nd dimension).

row_has_all_zeros = ~any(data, 2)

If you want the indices instead of the logical array, just apply find to the result:

indices = find(row_has_all_zeros);

Upvotes: 4

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