Calculate the Shannon entropy H of a given input string.
Given the discreet random variable $X$ that is a string of $N$ "symbols" (total characters) consisting of $n$ different characters (n=2 for binary), the Shannon entropy of X in bits/symbol is :
$H_2(X) = -\sum_{i=1}^n \frac{count_i}{N} \log_2 \left(\frac{count_i}{N}\right)$
where $count_i$ is the count of character $n_i$.
entropy
is a function.
testString: assert(typeof entropy === 'function', 'entropy
is a function.');
- text: entropy("0")
should return 0
testString: assert.equal(entropy('0'), 0, 'entropy("0")
should return 0
');
- text: entropy("01")
should return 1
testString: assert.equal(entropy('01'), 1, 'entropy("01")
should return 1
');
- text: entropy("0123")
should return 2
testString: assert.equal(entropy('0123'), 2, 'entropy("0123")
should return 2
');
- text: entropy("01234567")
should return 3
testString: assert.equal(entropy('01234567'), 3, 'entropy("01234567")
should return 3
');
- text: entropy("0123456789abcdef")
should return 4
testString: assert.equal(entropy('0123456789abcdef'), 4, 'entropy("0123456789abcdef")
should return 4
');
- text: entropy("1223334444")
should return 1.8464393446710154
testString: assert.equal(entropy('1223334444'), 1.8464393446710154, 'entropy("1223334444")
should return 1.8464393446710154
');
```