Summing up values of A matrix if it matches the same value in B

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JL 2019-8-27

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https://ww2.mathworks.cn/matlabcentral/answers/477725-summing-up-values-of-a-matrix-if-it-matches-the-same-value-in-b

评论： JL 2019-8-27

Hi everyone, I have 2 matrices A and B

A =[1;
    2;
    1;
    3;
    4;
    5;
    6;];
B = [40.5511;
     40.5511;
     34.6732;
     34.6731;
     32.1111;
     32.1111;
     32.1111;]

I want to create C by summing up the values in A if they have the same corresponding value in B.

 C = [3 40.5511;
34.6732;
34.6731;
32.1111;];

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采纳的回答

Alex Mcaulley 2019-8-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/477725-summing-up-values-of-a-matrix-if-it-matches-the-same-value-in-b#answer_389229

One option:

[G,ID] = findgroups(B);
C = [splitapply(@sum,A,G),ID]
C =
   15.0000   32.1111
    3.0000   34.6731
    1.0000   34.6732
    3.0000   40.5511

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Alex Mcaulley 2019-8-27

You can change the visualization of your command window using format. Do you mean this?

format short
C =
   15.0000   32.1111
    3.0000   34.6731
    1.0000   34.6732
    3.0000   40.5511
format long
C =
  15.000000000000000  32.111100000000000
   3.000000000000000  34.673099999999998
   1.000000000000000  34.673200000000001
   3.000000000000000  40.551099999999998