Ranking of numpy array with possible duplicates

Question

I have a numpy array of floats/ints and want to map its elements into their ranks.

If an array doesn\'t have duplicates the problem can be solved by the following co

Answer 1

You can do reasonably well using unique and bincount:

>>> u, v = np.unique(a2, return_inverse=True)
>>> (np.cumsum(np.bincount(v)) - 1)[v]
array([0, 3, 4, 5, 6, 3, 7, 9, 9, 3])

Or, for the minimum rank:

>>> (np.cumsum(np.concatenate(([0], np.bincount(v)))))[v]
array([0, 1, 4, 5, 6, 1, 7, 8, 8, 1])

There's a minor speedup by giving bincount the number of bins to provide:

(np.cumsum(np.bincount(v, minlength=u.size)) - 1)[v]