reduce the length by summing the bins

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Junaid
Junaid am 24 Jun. 2012
Kommentiert: Tamara del Águila am 23 Mai 2021
dear all,
Let say I have matrix of Histograms, where each column is one histogram vector. What I want is to sum two bins each other, i.e., first bin + second bin, Third bin + forth bin.
Let say
A =
[ 1 2 3
4 5 6
7 8 9
10 11 12]
output should be
B =
[ 5 7 9
17 19 21 ]
Is it possible without using loops.

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Walter Roberson
Walter Roberson am 24 Jun. 2012
B = A(1:2:end, :) + A(2:2:end,:);

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Jan
Jan am 24 Jun. 2012
Faster for large arrays, because it does not create temporary arrays, e.g. 3 times faster for [1e5 x 3] in Matlab 2009a/64/Win:
B = reshape(sum(reshape(A, 2, 2, 3)), 2, 3);
[EDITED] General approach:
newLen = size(A, 1) / 2;
B = reshape(sum(reshape(A, 2, newLen, 3)), newLen, 3);
See also: FEX: BlockMean
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Tamara del Águila
Tamara del Águila am 21 Mai 2021
... and how could I possibly downsample an array binning the data? With resample is not possible because it calculate averages, so I was wondering if it would be possible to do it with something like this answer, so that the matrix can be resize (let's say, to the half or less) without loosing the counts.
Tamara del Águila
Tamara del Águila am 23 Mai 2021
About what I further commented on the topic, In any case anyone is interested, has the same problem, or would like to share its knowledge about the specific issue, I have posted a formal question, because I am stuck with it...
https://nl.mathworks.com/matlabcentral/answers/837388-how-to-bin-data-from-a-matrix-2d-array?s_tid=srchtitle
thanks!

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