reduce the length by summing the bins

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Junaid
Junaid 2012-6-24
评论： Tamara del Águila 2021-5-23
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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采纳的回答

Walter Roberson
Walter Roberson 2012-6-24
B = A(1:2:end, :) + A(2:2:end,:);

更多回答（1 个）

Jan
Jan 2012-6-24
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 2021-5-21
... 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 2021-5-23
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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