MATLAB: Accumulate a matrix of counters

Question

I'm keeping a matrix of counters m. The indices of the individual counters to add to are kept in a (large) vector indx. What I am trying to accomplish is the behavior of:

for ii = i:length(indx)
  m(indx(ii)) = m(indx(ii)) + 1;
end;

but in a vectorized way. I tried:

m(indx) = m(indx) + 1

but that ignores multiple occurrences of the same index in 'indx' As an example, note the difference in outcome between:

m = zeros(5)
indx = [1 20 3 9 19 1 9 24 1 9];
m(indx) = m(indx) + 1

and

m = zeros(5);
indx = [1 20 3 9 19 1 9 24 1 9];
for ii = 1:length(indx)
  m(indx(ii)) = m(indx(ii)) + 1;
end;
disp(m);

Any ideas?

Answer 1

   m=reshape(accumarray(indx(:),1,[25,1]),[5,5])