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Extract the first negative value in a matrix column

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Thorsten
Thorsten 2013-5-29
I have a 501x100000 Matrix, containing positive and some negative values. The values were calculated using random numbers. I need the value, not the index of the first negative entry in each column. If there is no negative value in the column it should be displayed by a 0.
simplified example:
A = [ 1, 2, 5, 6; -1, 4, 8,-4; -2, 3, 9, 1; -2,-1, 3,-1 ]
The answer I need (for that example) is:
-1,-1,0,-4
Thanks in advance for any help...

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2013-5-29
编辑：Azzi Abdelmalek 2013-5-29
Edit
out=arrayfun(@(x) min([ 0 A(find(A(:,x)<0,1),x)]),1:size(A,2))

更多回答（2 个）

Iain
Iain 2013-5-29
for i = 1:cols
Answer = A(find(A(:,i)<0,1),i);
if isempty(Answer)
Out(i) = 0;
else
Out(i) = Answer;
end
end
Andrei Bobrov
Andrei Bobrov 2013-5-29
t = A < 0;
[~,jj] = find(t);
out = accumarray(jj,A(t),[],@(x)x(1))';

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