Sum according to the values in another column

Hi everyone,

I have two columns, with the same amount of elements.

C1 = 1-1-1-1-1-2-2-2-2-2-2-3-3-3-4-4-4-4

C2 = 5-10-12-35-3-1-4-26-5-11-12-8-2-22-8-2-5-7

I would like to sum the values of C2 according to C1, and present the results like that:

1 - 65;

2 - 59

3 - 32

4 - 22

How can I do that?

Answer 1

[Steven Lord]

Use groupsummary.

C1 = [1 1 1 1 1 2 2 2 2 2 2 3 3 3 4 4 4 4].';
C2 = [5 10 12 35 3 1 4 26 5 11 12 8 2 22 8 2 5 7].';

[binvalues, bingroups] = groupsummary(C2, C1, @sum)

This applies the sum function to each group of elements in C2 for which the corresponding values in C1 are the same. Each element of binvalues is the sum of the elements in C2 for the bin in the corresponding element of bingroups.

The elements of C1 don't need to be positive integers; I could have grouped the values corresponding to bins associated with C1+1.5 if I wanted.

[Aragorn23]

Thank you Steven.

Answer 2

[madhan ravi]

[u,~,idx]=unique(C1(:));
Wanted = [u,accumarray(idx,C2,[],@sum)]

[Guillaume]

sum is the default function for accumarray, so

wanted = [u, accumarray(idx, C2)]

would produce the same result.

[madhan ravi]

Oh thank you Guillaume :)

[Aragorn23]

Thank you, guys.