Combine elements across two vectors

I have two vectors, such that one is the time index and the second is how many times it occurred:

m=[10 20 20 30] n=[3 4 5 6]

I would like to combine, the two occurrences at time 20.

Essentially I need:

m=[10 20 30] n=[3 9 6] <-- here 4+5 were added because they both occurred in time 20.

Any suggestions on how to achieve this with code? I am trying to avoid a for loop...

Thanks in advance!

Answer 1

[Guillaume]

[m, ~, indices] = unique(m, 'stable'); %stable optional if you don't mind your data sorted
n = accumarray(indices, n)';

[Alexandra Maxim]

Thank you so much! it worked brilliantly