entropy.py

#!/usr/bin/env python
"""Computes entropy of a sequence of messages
"""
from __future__ import division
from collections import Counter
from math import log


def entropy(sequence):
    res = 0
    n = len(sequence)
    counts = Counter(sequence).values()
    for count in counts:
        res -= (count / n) * (log(count, 2) - log(n, 2))
    return res


if __name__=="__main__":
    print entropy([1, 2, 1, 1, 1, 1])
    print entropy([1, 1, 1, 1, 1, 1])
    print entropy([1, 1, 1, 2, 2, 2])