Entropy
You are encouraged to solve this task according to the task description, using any language you may know.
Calculate the entropy (shannon entropy) of a given input string. Use "1223334444" as an example. The result should be around 1.84644 bit.
Burlesque
<lang burlesque> blsq ) "1223334444"F:u[vv^^{1\/?/2\/LG}m[?*++ 1.8464393446710157 </lang>
D
<lang d>import std.stdio, std.algorithm, std.math;
double entropy(T)(T[] s) /*pure nothrow*/ if (__traits(compiles, sort(s))) {
return s
.sort()
.group
.map!(g => g[1] / cast(double)s.length)
.map!(p => -p * log2(p))
.reduce!q{a + b};
}
void main() {
"1223334444"d.dup.entropy.writeln;
}</lang>
- Output:
1.84644
Haskell
<lang haskell> import Data.List
main = print $ entropy "1223334444"
entropy s =
sum . map lg' . fq' . map (fromIntegral.length) . group . sort $ s
where lg' c = (c * ) . logBase 2 $ 1.0 / c
fq' c = map (\x -> x / (sum c)) c
</lang>
J
Solution:<lang j> entropy=: +/@:-@(* 2&^.)@(#/.~ % #)</lang> Example:<lang j> entropy '1223334444' 1.84644</lang>
Perl
<lang Perl>sub entropy {
my %count; $count{$_}++ for @_;
my @p = map $_/@_, values %count;
my $entropy = 0;
$entropy += - $_ * log $_ for @p;
$entropy / log 2
}
print entropy split //, "1223334444";</lang>
Perl 6
<lang Perl 6>sub entropy(@a) {
- [+] map -> $p { $p * log $p },
@a.classify({$_}).map: *.value.elems / @a.elems;
}
say log(2) R/ entropy '1223334444'.comb;</lang>