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

creatematrixsum

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;
      1 34.6732;
      3 34.6731;
     15 32.1111;];

Best Answer

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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