vector confusion

I have a vector A whose values are indices for vector P.

Say A = 2 occurs 10 times.

If I do:

P(A) = P(A) + 1

P(2) = 1 % not 10

I believe I understand why this is happening. Is there a solution without going into FOR loops? A could be quite large.

[the cyclist]

I do not understand what you mean by "A = 2 occurs 10 times". Can you write out code for what you mean?

[Leor Greenberger]

A = [1 2 4 5 2 4 6 7 2 ....] <-- 2 occurs 10 times.

Answer 1

[Walter Roberson]

Especially if you are starting with an all-zero array, use

P = accumarray(A(:),1);

[Leor Greenberger]

excellent!!! I can't believe there is a function for this!