Calculate median values of slices of array associated with histogram bins

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dormant 2023-11-15

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https://ww2.mathworks.cn/matlabcentral/answers/2047627-calculate-median-values-of-slices-of-array-associated-with-histogram-bins

评论： Star Strider 2023-11-15

I have an array (array1) which I want to put into histogram bins. I have a second array (array2) which is the same length.

I can sum the values of array2 in each bin with this:

[count, edges, idx] = histcounts(array1,edges);
binsums = accumarray(idx,array2);

But how can I calculate the median values of array2 in each bin?

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Answer 1

Star Strider 2023-11-15

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I would use another accumarray call:

binmedians = accumarray(idx+1, (1:numel(idx)).', [], @(x)median(array2(x)))

Creating data and correcting for ‘idx’ having 0 for some elements (making them inappropriate index values) —

array1 = randn(1E+3,1);
array2 = randn(1E+3,1);
edges = 1:9;
[count, edges, idx] = histcounts(array1,edges);
binsums = accumarray(idx+1,array2)
binsums = 4×1
  -13.0331
   20.8357
   -1.5279
   -2.0722
binmedians = accumarray(idx+1, (1:numel(idx)).', [], @(x)median(array2(x)))
binmedians = 4×1
   -0.0237
    0.2213
    0.1113
   -1.0361