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JT5D/Shannon-Entropy.js

Created April 10, 2020 03:54
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  1. JT5D created this gist Apr 10, 2020.
    19 changes: 19 additions & 0 deletions Shannon-Entropy.js
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    Original file line number Diff line number Diff line change
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    // Shannon entropy in bits per symbol.
    function entropy(str) {
    const len = str.length

    // Build a frequency map from the string.
    const frequencies = Array.from(str)
    .reduce((freq, c) => (freq[c] = (freq[c] || 0) + 1) && freq, {})

    // Sum the frequency of each character.
    return Object.values(frequencies)
    .reduce((sum, f) => sum - f/len * Math.log2(f/len), 0)
    }

    console.log(entropy('1223334444')) // 1.8464393446710154
    console.log(entropy('0')) // 0
    console.log(entropy('01')) // 1
    console.log(entropy('0123')) // 2
    console.log(entropy('01234567')) // 3
    console.log(entropy('0123456789abcdef')) // 4