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时间:2015-06-03 13:28:48      阅读:244      评论:0      收藏:0      [点我收藏+]

计算数据集的香农熵

from math import log
def calcShannonEnt(dataSet):
    numEntries = len(dataset)
    labelCounts = {}
    for featVec in dataset:
        currentLabel = featVec[-1]
        if currentLabel not in labelCounts.keys():
            labelCountspcurrentLabel] = 0
        labelCounts[currentLabel] += 1
    shannonEnt = 0.0
    for key in labelCounts:
        prob = float(labelCounts[key])/numEntries
        shannonEnt -= prob * log(prob,2)
    return shannonEnt

 H=-∑p(xi)log(2,p(xi)) (i=1,2,..n)

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原文:http://www.cnblogs.com/battle-lee/p/4548768.html

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