How to vectorize this code with logical idexing

2014 5 14
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更新时间：2014 5 15
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Hi all,
I have the following code, how can I avoid the for to make it faster?
a=[10:5:50];
b=[10:20:50];
c=rand(size(a));
for i=length(b)-1
d=c(a>=b(i) & a<b(i+1));
end
thanks
cheers

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Jos (10584)
Jos (10584) 2014-5-15
Since you're only storing the last values of d in each iteration, you can skip the for-loop completely:
i = length(b)-1
d = c(a>=b(i)) & a<b(i+1))
but I am pretty sure you intend to do something else.
What should happen with the values of d obtained in the iterations 1 to length(b)-2?

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Andrei Bobrov
Andrei Bobrov 2014-5-14
编辑：Andrei Bobrov 2014-5-15

0 个投票

a=[10:5:50];
b=[10:20:50];
c=rand(size(a));
[~,ii] = histc(a,b);
d = accumarray(ii(:),c(:),size(b(:)),@(x){x})

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pietro
pietro 2014-5-15
编辑：pietro 2014-5-15
Hi Andrei,
thanks. I tried with my code but the empty bins at the end of the array are skipped. Here an axample:
a=[10:5:20, 55:5:90];
b=[10:20:170];
c=rand(size(a));
[er,ii] = histc(a,b);
d = accumarray(ii(:),c(:),[],@(x){x});
d should be a 8 elements array instead it is 4 elements array. How could I do to take into account the empty bins at the end of the array?

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