Find values in a matrix and put them into a vector
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08-10-2019 - |
Question
It must be simple, but surprisingly I couldn't find an answer to this problem here or by trial-and-error.
I want to get values out of a matrix (according to some condition) and place the values into a vector. I also need the subscript indices of the matching values. There is a lot of data so for loops are out.
This is a correct (but iterative) answer:
[I,J] = find(A > 5);
values = zeros(numel(I),1);
for i=1:numel(I)
values(i) = A(I(i),J(i));
end
I tried values = A(I,J)
but this is n-by-n instead of n-by-1.
Solution
You can implicitly treat the matrix like a vector (linear indexing):
I = find(A > 5);
values = A(I);
Note that you can do this more efficiently with logical indexing:
values = A(A > 5);
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