Averaging values in rank orderings with repeats

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Paul Fishback
Paul Fishback 2013-9-24
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.

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Kelly Kearney
Kelly Kearney 2013-9-24
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)
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Paul Fishback
Paul Fishback 2013-9-24
Thanks! Not only for such a quick answer, but also for introducing me to the accumarray command.
Paul Fishback
Paul Fishback 2013-9-24
The first argument for accumarray has to be a vector of positive integers. What if this were not the case for my vector u?

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