Efficient way to count unique elements in array in numpy/scipy in Python

Question

I have a scipy array, e.g.

a = array([[0, 0, 1], [1, 1, 1], [1, 1, 1], [1, 0, 1]])

I want to count the number of occurrences of each unique ele

Answer 1

If sticking with Python 2.7 (or 3.1) is not an issue and any of these two Python versions is available to you, perhaps the new collections.Counter might be something for you if you stick to hashable elements like tuples:

>>> from collections import Counter
>>> c = Counter([(0,0,1), (1,1,1), (1,1,1), (1,0,1)])
>>> c
Counter({(1, 1, 1): 2, (0, 0, 1): 1, (1, 0, 1): 1})

I haven't done any performance testing on these two approaches, though.