Conditional cumsum - how to create?
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This is probably easy, but my brain isn't working today...
How can you do the following operation in a vectorized way? I'd think it should be possible with some combination of cumsum, diff & logical indexing:
input = rand(10,1);
output = zeros(size(input);
output(1) = input(1);
for ind = 2:numel(input)
dif = input(ind) - input(ind-1);
if dif < 0
output(ind) = output(ind-1) + dif;
else
output(ind) = output(ind-1);
end
end
2 Commenti
the cyclist
il 2 Apr 2013
It would be useful if you also described conceptually what you are trying to do.
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Matt Tearle
il 2 Apr 2013
There may be better ways, but this works:
d = [true;diff(input)<0];
idx = find(d);
output = input(idx(cumsum(d)));
When the array is large enough, there's a pretty decent speedup (~50x)
5 Commenti
Sean de Wolski
il 2 Apr 2013
As you know, the DWIM Toolbox still hasn't been released to the public.
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