Averaging values in rank orderings with repeats

I'm wondering if there is a straightforward way for me to complete the following task.

Suppose u=[1,3,2,2,4,7,2,5] and I wish to create a vector of rank orderings that accounts for the fact that the three 2's are tied for ranks 2, 3, and 4 by using the average of these three ranks, (2+3+4)/3=3 in each corresponding entry.

More specifically, I want the rank ordering vector to be [1,5,3,3,6,8,3,7]. Notice how there is no 2 and no 4.

Answer 1

[Kelly Kearney]

The accumarray function should do what you want:

 u = [1,3,2,2,4,7,2,5];
 nu = length(u);
 rank = (1:nu)';

 ravg = accumarray(sort(u'), rank, [nu 1], @mean);
 ravg(u)

[Paul Fishback]

Thanks! Not only for such a quick answer, but also for introducing me to the accumarray command.

[Paul Fishback]

The first argument for accumarray has to be a vector of positive integers. What if this were not the case for my vector u?