20 lines
443 B
Lua
20 lines
443 B
Lua
function log2 (x) return math.log(x) / math.log(2) end
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function entropy (X)
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local N, count, sum, i = X:len(), {}, 0
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for char = 1, N do
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i = X:sub(char, char)
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if count[i] then
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count[i] = count[i] + 1
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else
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count[i] = 1
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end
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end
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for n_i, count_i in pairs(count) do
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sum = sum + count_i / N * log2(count_i / N)
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end
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return -sum
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end
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print(entropy("1223334444"))
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