How to count the frequency of the elements in an unordered list?

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In Python 2.7 (or newer), you can use collections.Counter:

import collections

a = [1,1,1,1,2,2,2,2,3,3,4,5,5]
counter=collections.Counter(a)

print(counter)
# Counter({1: 4, 2: 4, 3: 2, 5: 2, 4: 1})

print(counter.values())
# [4, 4, 2, 1, 2]

print(counter.keys())
# [1, 2, 3, 4, 5]

print(counter.most_common(3))
# [(1, 4), (2, 4), (3, 2)]

print(dict(counter))
# {1: 4, 2: 4, 3: 2, 5: 2, 4: 1}

If you are using Python 2.6 or older, you can download it here.

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