How to sum data in 2nd column for same values in column 1:

c = [11 1;
     11 3;
     12 5;
     13 9;
     13 11;
     13 3]

expected result is:

r = [11 4;
     12 5;
     13 23]

I know how to manage this using a loop but is there another easier way? In Matlab the function accumarray would work but is there something similar in Scilab?
Thanks.