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

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;];

Answer 1

[Alex Mcaulley]

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

[JL]

Thank you!

[JL]

Hi Alex, do you how I can make matrix A with 10 decimal points? like num2str? will it affect the code?

[Alex Mcaulley]

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

[JL]

thanks!