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jonasfj/entropy.dart

Created April 24, 2021 10:30
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How compute shannon entropy of a string in Dart.
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entropy.dart
// Copyright 2021 Google LLC.
// SPDX-License-Identifier: Apache-2.0
import 'dart:math';
double entropy(String s) {
final length = s.length.toDouble();
// TODO: Explore if this could be done faster without any allocations, since strings are often short.
final frequencies = <int, int>{};
for (final rune in s.runes) {
frequencies[rune] = (frequencies[rune] ?? 0) + 1;
}
var sum = 0.0;
for (final frequency in frequencies.values) {
sum -= frequency / length * (log(frequency / length) / log(2));
}
return sum;
}
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