32 lines
891 B
JavaScript
32 lines
891 B
JavaScript
(function(shannon) {
|
|
// Create a dictionary of character frequencies and iterate over it.
|
|
function process(s, evaluator) {
|
|
var h = Object.create(null), k;
|
|
s.split('').forEach(function(c) {
|
|
h[c] && h[c]++ || (h[c] = 1); });
|
|
if (evaluator) for (k in h) evaluator(k, h[k]);
|
|
return h;
|
|
};
|
|
// Measure the entropy of a string in bits per symbol.
|
|
shannon.entropy = function(s) {
|
|
var sum = 0,len = s.length;
|
|
process(s, function(k, f) {
|
|
var p = f/len;
|
|
sum -= p * Math.log(p) / Math.log(2);
|
|
});
|
|
return sum;
|
|
};
|
|
})(window.shannon = window.shannon || {});
|
|
|
|
// Log the Shannon entropy of a string.
|
|
function logEntropy(s) {
|
|
console.log('Entropy of "' + s + '" in bits per symbol:', shannon.entropy(s));
|
|
}
|
|
|
|
logEntropy('1223334444');
|
|
logEntropy('0');
|
|
logEntropy('01');
|
|
logEntropy('0123');
|
|
logEntropy('01234567');
|
|
logEntropy('0123456789abcdef');
|