Weighted mean by groups

Question

Maximilian Schwarz 2022-9-28

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1813810-weighted-mean-by-groups

编辑： dpb 2022-9-28

I am trying to get the weighted mean of values by group id but I don't undersnatnd why my ouput (Mean) is a matrix and not a vector.

id = { 'a'; 'a'; 'b'; 'b'; 'c'; 'c'};
values = [1;2;3;4;5;6];
weights = [0.5;0.7;0.3;0.4;0.5;0.1];
exampletable = table(id, weights, values);
G = findgroups(exampletable.id);
wmean = @(w,v)w'.*mean(v);
Mean = splitapply(wmean, exampletable.weights, exampletable.values, G)

id = { 'a'; 'a'; 'b'; 'b'; 'c'; 'c'};

values = [1;2;3;4;5;6];

weights = [0.5;0.7;0.3;0.4;0.5;0.1];

exampletable = table(id, weights, values);

G = findgroups(exampletable.id);

wmean = @(w,v)w'.*mean(v);

Mean = splitapply(wmean, exampletable.weights, exampletable.values, G)

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Answer 1

dpb 2022-9-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1813810-weighted-mean-by-groups#answer_1062555

编辑：dpb 2022-9-28

在 MATLAB Online 中打开

It's the wmean function definition that's doing it -- what you intended was

wmean = @(w,v)mean(w.*v);

trying that,

id = { 'a'; 'a'; 'b'; 'b'; 'c'; 'c'};
values = [1;2;3;4;5;6];
weights = [0.5;0.7;0.3;0.4;0.5;0.1];
exampletable = table(id, weights, values);
G = findgroups(exampletable.id);
Mean = splitapply(wmean, exampletable.weights, exampletable.values, G)
Mean = 3×1
    0.9500
    1.2500
    1.5500

ADDENDUM

OBTW, you can do things like this without the explicit step of findgroups with groupsummary (or several other ways, as well)--

gmeans=groupsummary(exampletable,'id',wmean,{"weights","values"})
gmeans = 3×3 table
     id      GroupCount    fun1_weights_values
    _____    __________    ___________________

    {'a'}        2                0.95        
    {'b'}        2                1.25        
    {'c'}        2                1.55        