Entropy

editable example

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ghul

use IO.Std.write_line

use Collections.MAP

use Ghul.Pipes

use System.Math

entropy(text: string) -> double is

let counts = MAP[char, int]()

for character in text do

let seen mut = 0

counts.try_get_value(character, seen ref)

counts[character] = seen + 1

od

let total = cast double(text.length)

return counts.values

|> map(count => cast double(count) / total)

|> reduce(0.0D, (bits, probability) =>

bits - probability * Math.log2(probability))

si

let text = "1223334444"

write_line("{text}: {entropy(text)} bits/symbol")

1223334444: 1.8464393446710154 bits/symbol