Map each list value to its corresponding percentile

Question

I\'d like to create a function that takes a (sorted) list as its argument and outputs a list containing each element\'s corresponding percentile.

For example,

Answer 1

Pure numpy version of Kevin's solution

As Kevin said, optimal solution works in O(n log(n)) time. Here is fast version of his code in numpy, which works almost the same time as stats.rankdata:

percentiles = numpy.argsort(numpy.argsort(array)) * 100. / (len(array) - 1)

PS. This is one if my favourite tricks in numpy.