Sum only consecutive positive numbers...

Hi all, I need help. So, I have this vector:

 l = [1 2 -3 4 -5 6 7 -8 9 10 11 12];

I need sum only consecutive positive numbers. when picking up a negative number, put NaN. So, the results correct is:

a = [3 NaN 4 NaN 13 NaN 42];

Thank you!

Best regards.

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

Answer 1

[ANKUR KUMAR]

A = [1 2 -3 4 -5 6 7 -8 9 10 11 12];
A(A<=0)=nan;
nansum(A)

[Walter Roberson]

No, this gives a grand total of the positive values, rather than giving the required output vector.

[ANKUR KUMAR]

Ops, Sorry. I misread the question.

Answer 2

[Image Analyst]

Here's one way:

m = [1 2 -3 4 -5 6 7 -8 9 10 11 12]
dm = [1. diff(m)]
mask = (m > 0) & (dm >= 0)
props = regionprops(mask, m, 'Area', 'MeanIntensity');
sums = [props.Area] .* [props.MeanIntensity]
% Add in nan's
sums = [sums; nan(1, length(sums))]
sums = sums(:)'
% Get rid of last nan.
sums = sums(1:end-1)

Answer 3

[Andrei Bobrov]

l = [1 2 -3 4 -5 6 7 -8 9 10 11 12];

lo = l > 0;
h = cumsum(diff([0;lo(:)]) == 1).*lo(:);
S = accumarray(h + 1,l);
out = nan(numel(S)*2-1,1);
out(1:2:end) = S;

or

l = [1 2 -3 4 -5 6 7 -8 9 10 11 12];

lo = l > 0;
h = diff([~lo(1),lo])~=0;
out = accumarray(cumsum(h(:)),l);
out(out < 0) = nan;