How do I take the average of elements of a vector depending on the values of another vector?

Question

L'O.G. 2022-8-28

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评论： Torsten 2022-8-28

Given two vectors, how do I take the average of values in one vector depending on what the value is in the second vector?

For example:

A = [2 3 2 2 3 4 3 3];

B = [0.1 0.2 0.22 0.13 0.07 0.88 0.3 0.5];

Here, I'd want to take the average of elements 1, 3, and 4 in B because they correspond to A = 2, and then similarly elements 2, 5, 7, and 8 in B that correspond to A = 3, and then element 6 corresponding tto A = 4.

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Answer 1

Torsten 2022-8-28

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编辑：Torsten 2022-8-28

在 MATLAB Online 中打开

A = [2 3 2 2 3 4 3 3];
B = [0.1 0.2 0.22 0.13 0.07 0.88 0.3 0.5];
Au = unique(A,'stable');
C = arrayfun(@(i)mean(B(A==Au(i))),1:numel(Au))
C = 1×3
    0.1500    0.2675    0.8800

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Torsten 2022-8-28

编辑：Torsten 2022-8-28

在 MATLAB Online 中打开

I modified the answer from

Au = unique(A);

to

Au = unique(A,'stable');

for that the mean values are sorted according to the values appearing in A.

I don't know if this is important for your application.

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Answer 2

Paul 2022-8-28

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https://ww2.mathworks.cn/matlabcentral/answers/1789155-how-do-i-take-the-average-of-elements-of-a-vector-depending-on-the-values-of-another-vector#answer_1036210

在 MATLAB Online 中打开

This common workflow is discussed here: splitapply

A = [2 3 2 2 3 4 3 3];
B = [0.1 0.2 0.22 0.13 0.07 0.88 0.3 0.5];
[G,ID]=findgroups(A);
groupmean = splitapply(@mean,B,G);
table(ID.',groupmean.','VariableNames',{'ID' , 'GroupMean'})
ans = 3×2 table
    ID    GroupMean
    __    _________

    2        0.15  
    3      0.2675  
    4        0.88  