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How to calculate sum of specific array elements

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Jim
Jim on 6 Nov 2012
Let's say you have two arrays of the same size: one with the data (x) and one carrying some indices that characterize the data (q)
For example: x = [ 3 5 2 10 6 4] q = [ 0 0 1 2 3 3]
This means the first two elements of (x) belong to the same category indicated by 0 and so on.
How to calculate the sums of elements in (x) which belong to the same category i.e. the same integer number as specified by (q).
The result for the above example should be: r = [ 8 2 10 10 ]
Is this possible without using a loop?

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Accepted Answer

Kye Taylor
Kye Taylor on 6 Nov 2012
Edited: Kye Taylor on 6 Nov 2012
Try
x = [ 3 5 2 10 6 4]';
q = [ 0 0 1 2 3 3]';
% note first input must be column vector with positive integers (indices)
yourSums = accumarray(q+1,x);

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