Sum all negative values in a matrix
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I have a matrix that is 400x95. I would like to sum all the negative values in each column and divide this by the sum of all the positive values in the same column to yield a new vector that is essentially 1x95. Any help is much appreciated!
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John D'Errico
2015-6-1
编辑：John D'Errico
2015-6-1
Too trivial?
sum(A.*(A < 0),1)./sum(A.*(A > 0),1)
The point is, to learn to start to think in terms of matrices and vectors, and operations on those objects.
Of course, be careful if there are no positive elements in a column of the array. In that case, you will get either an Inf or NaN result, depending on if there are any negative values in that column.
2 个评论
Joseph Cheng
2015-6-1
2nd method would used the 2nd input parameter in max() and min().
x = magic(10)-50;
rat = sum(min(x,0))./sum(max(x,0))
John D'Errico
2015-6-1
Another good way. There are always so many ways to solve a problem like this, once you start thinking in terms of arrays.
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