# Entropy/Narcissist

Entropy/Narcissist
You are encouraged to solve this task according to the task description, using any language you may know.

Write a computer program that computes and shows its own   entropy.

```with Ada.Text_Io;

procedure Entropy is

type Hist_Type is array (Character) of Natural;

function Log_2 (V : Float) return Float is
begin
return Log (V) / Log (2.0);
end Log_2;

procedure Read_File (Name : String; Hist : out Hist_Type) is
File : File_Type;
Char : Character;
begin
Hist := (others => 0);
Open (File, In_File, Name);
while not End_Of_File (File) loop
Get (File, Char);
Hist (Char) := Hist (Char) + 1;
end loop;
Close (File);

function Length_Of (Hist : Hist_Type) return Natural is
Sum : Natural := 0;
begin
for V of Hist loop
Sum := Sum + V;
end loop;
return Sum;
end Length_Of;

function Entropy_Of (Hist : Hist_Type) return Float is
Length : constant Float := Float (Length_Of (Hist));
Sum    : Float := 0.0;
begin
for V of Hist loop
if V > 0 then
Sum := Sum + Float (V) / Length * Log_2 (Float (V) / Length);
end if;
end loop;
return -Sum;
end Entropy_Of;

package Float_Io is new Ada.Text_Io.Float_Io (Float);
Name : constant String := Ada.Command_Line.Argument (1);
Hist : Hist_Type;
Entr : Float;
begin
Float_Io.Default_Exp := 0;
Float_Io.Default_Aft := 6;

Entr := Entropy_Of (Hist);

Put ("Entropy of '");
Put (Name);
Put ("' is ");
Float_Io.Put (Entr);
New_Line;
end Entropy;
```
Output:
`Entropy of 'entropy.adb' is  4.559854`

## ALGOL 68

Assumes the source file is in the current directory and called "entropyNarcissist.a68".
Note that the source here uses spaces, not tabs, hence the low entropy, replacing all runs of four spaces with a single space results in an entropy of +4.64524532762062e +0.

```BEGIN
# calculate the shannon entropy of a string                                #
PROC shannon entropy = ( STRING s )REAL:
BEGIN
INT string length = ( UPB s - LWB s ) + 1;
# count the occurances of each character #
[ 0 : max abs char ]INT char count;
FOR char pos FROM LWB char count TO UPB char count DO
char count[ char pos ] := 0
OD;
FOR char pos FROM LWB s TO UPB s DO
char count[ ABS s[ char pos ] ] +:= 1
OD;
# calculate the entropy, we use log base 10 and then convert #
# to log base 2 after calculating the sum                    #
REAL entropy := 0;
FOR char pos FROM LWB char count TO UPB char count DO
IF char count[ char pos ] /= 0
THEN
# have a character that occurs in the string #
REAL probability = char count[ char pos ] / string length;
entropy -:= probability * log( probability )
FI
OD;
entropy / log( 2 )
END; # shannon entropy #

IF  FILE input file;
STRING file name = "entropyNarcissist.a68";
open( input file, file name, stand in channel ) /= 0
THEN
# failed to open the file #
print( ( "Unable to open """ + file name + """", newline ) )
ELSE
# file opened OK #
BOOL at eof := FALSE;
# set the EOF handler for the file #
on logical file end( input file
, ( REF FILE f )BOOL:
BEGIN
# note that we reached EOF on the latest read #
at eof := TRUE;
# return TRUE so processing can continue #
TRUE
END
);
# construct a string containing the whole file #
STRING file contents := "";
WHILE STRING line;
get( input file, ( line, newline ) );
NOT at eof
DO
file contents +:= line + REPR 12
OD;
close( input file );
# show the entropy of the file cotents #
print( ( shannon entropy( file contents ), newline ) )
FI
END```
Output:
```+3.93440186690189e  +0
```

## AutoHotkey

Works with: AutoHotkey 1.1
```FileRead, var, *C %A_ScriptFullPath%
MsgBox, % Entropy(var)

Entropy(n) {
a := [], len := StrLen(n), m := n
while StrLen(m) {
s := SubStr(m, 1, 1)
m := RegExReplace(m, s, "", c)
a[s] := c
}
for key, val in a {
m := Log(p := val / len)
e -= p * m / Log(2)
}
return, e
}
```
Output:
`5.942956`

## AWK

The record separator RS is set to end of file. So getline reads the whole file in one line.

```BEGIN{FS=""
RS="\x04"#EOF
getline<"entropy.awk"
for(i=1;i<=NF;i++)H[\$i]++
for(i in H)E-=(h=H[i]/NF)*log(h)
print "bytes ",NF," entropy ",E/log(2)
exit}
```
Output:
`bytes  158  entropy  5.2802`

## BBC BASIC

```      DIM Freq%(255)
FOR I%=PAGE TO LOMEM Freq%(?I%)+=1 NEXT
Size=LOMEM - PAGE
FOR I%=0 TO 255
IF Freq%(I%) Entropy+=Freq%(I%) / Size * LN(Freq%(I%) / Size) / LN(2)
NEXT
PRINT "My size is ";Size " bytes and my entropy is ";-Entropy "!"
END
```
Output:
`My size is 224 bytes and my entropy is 5.11257089!`

## C

Minor edit to the Entropy answer.

Assumes that the source file is stored in the working directory as "entropy.c".

```#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <math.h>

#define MAXLEN 961 //maximum string length

int makehist(char *S,int *hist,int len){
int wherechar[256];
int i,histlen;
histlen=0;
for(i=0;i<256;i++)wherechar[i]=-1;
for(i=0;i<len;i++){
if(wherechar[(int)S[i]]==-1){
wherechar[(int)S[i]]=histlen;
histlen++;
}
hist[wherechar[(int)S[i]]]++;
}
return histlen;
}

double entropy(int *hist,int histlen,int len){
int i;
double H;
H=0;
for(i=0;i<histlen;i++){
H-=(double)hist[i]/len*log2((double)hist[i]/len);
}
return H;
}

int main(void){
char S[MAXLEN];
int len,*hist,histlen;
double H;
FILE *f;
f=fopen("entropy.c","r");
for(len=0;!feof(f);len++)S[len]=fgetc(f);
S[--len]='\0';
hist=(int*)calloc(len,sizeof(int));
histlen=makehist(S,hist,len);
//hist now has no order (known to the program) but that doesn't matter
H=entropy(hist,histlen,len);
printf("%lf\n",H);
return 0;
}
```
Output:
```5.195143
```

## C++

```#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

string contents;
string line;
ifstream inFile(path);
while (getline (inFile, line)) {
contents.append(line);
contents.append("\n");
}
inFile.close();
return contents;
}

double entropy (string X) {
const int MAXCHAR = 127;
int N = X.length();
int count[MAXCHAR];
double count_i;
char ch;
double sum = 0.0;
for (int i = 0; i < MAXCHAR; i++) count[i] = 0;
for (int pos = 0; pos < N; pos++) {
ch = X[pos];
count[(int)ch]++;
}
for (int n_i = 0; n_i < MAXCHAR; n_i++) {
count_i = count[n_i];
if (count_i > 0) sum -= count_i / N * log2(count_i / N);
}
return sum;
}

int main () {
return 0;
}
```
Output:
`4.58688`

## Crystal

Translation of: Ruby
```def entropy(s)
counts = s.chars.each_with_object(Hash(Char, Float64).new(0.0)) { |c, h| h[c] += 1 }
counts.values.sum do |count|
freq = count / s.size
-freq * Math.log2(freq)
end
end

```
Output:
```4.963709090807145
```

## D

```void main(in string[] args) {
import std.stdio, std.algorithm, std.math, std.file;

return data
.group
.map!(g => g[1] / double(data.length))
.map!(p => -p * p.log2)
.sum
.writeln;
}
```
Output:
`6.29803`

## Elixir

```File.open(__ENV__.file, [:read], fn(file) ->
leng = String.length(text)
String.codepoints(text)
|> Enum.group_by(&(&1))
|> Enum.map(fn{_,value} -> length(value) end)
|> Enum.reduce(0, fn count, entropy ->
freq = count / leng
entropy - freq * :math.log2(freq)
end)
|> IO.puts
end)
```
Output:
```4.848342673395324
```

## Emacs Lisp

```(defun shannon-entropy (input)
(let ((freq-table (make-hash-table))
(entropy 0)
(length (+ (length input) 0.0)))
(mapcar (lambda (x)
(puthash x
(+ 1 (gethash x freq-table 0))
freq-table))
input)
(maphash (lambda (k v)
(set 'entropy (+ entropy
(* (/ v length)
(log (/ v length) 2)))))
freq-table)
(- entropy)))

(defun narcissist ()
(shannon-entropy (with-temp-buffer
(insert-file-contents "U:/rosetta/narcissist.el")
(buffer-string))))
```
Output:
```(narcissist)
4.5129548515535785
```

## Erlang

```#! /usr/bin/escript

-define(LOG2E, 1.44269504088896340735992).

main(_) ->
Self = escript:script_name(),
io:format("My entropy is ~p~n", [entropy(Contents)]).

entropy(Data) ->
Frq = count(Data),
maps:fold(fun(_, C, E) ->
P = C / byte_size(Data),
E - P*math:log(P)
end, 0, Frq) * ?LOG2E.

count(Data) -> count(Data, 0, #{}).
count(Data, I, Frq) when I =:= byte_size(Data) -> Frq;
count(Data, I, Frq) ->
Chr = binary:at(Data, I),
case Frq of
#{Chr := K} -> count(Data, I+1, Frq #{Chr := K+1});
_ -> count(Data, I+1, Frq #{Chr => 1})
end.
```
Output:
```My entropy is 5.00988934931771
```

## Factor

```USING: assocs io io.encodings.utf8 io.files kernel math
math.functions math.statistics prettyprint sequences ;
IN: rosetta-code.entropy-narcissist

: entropy ( seq -- entropy )
[ length ] [ histogram >alist [ second ] map ] bi
[ swap / ] with map
[ dup log 2 log / * ] map-sum neg ;

"entropy-narcissist.factor" utf8 [
contents entropy .
```
Output:
```4.591946214804276
```

## FreeBASIC

```' version 01-06-2016
' compile with: fbc -s console
' modified code from ENTROPY entry

Dim As Integer i, count, totalchar(255)
Dim As UByte buffer
Dim As Double prop, entropy
' command (0) returns the name of this program (including the path)
Dim As String slash, filename = Command(0)
Dim As Integer ff = FreeFile   ' find first free filenumber
Open filename For Binary As #ff

If Err > 0 Then ' should not happen
Print "Error opening the file"
Beep : Sleep 5000, 1
End
End If

' will read 1 UByte from the file until it reaches the end of the file
For i = 1 To Lof(ff)
Get #ff, ,buffer
totalchar(buffer) += 1
count = count + 1
Next

For i = 0  To 255
If totalchar(i) = 0 Then Continue For
prop = totalchar(i) / count
entropy = entropy - (prop * Log (prop) / Log(2))
Next

' next lines are only compiled when compiling for Windows OS (32/64)
#Ifdef __FB_WIN32__
slash = chr(92)
print "Windows version"
#endif
#Ifdef __FB_LINUX__
slash = chr(47)
print "LINUX version"
#EndIf

i = InStrRev(filename, slash)
If i <> 0 Then filename = Right(filename, Len(filename)-i)

Print "My name is "; filename
Print : Print "The Entropy of myself is"; entropy
Print

' empty keyboard buffer
While InKey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End```
Output:
```Windows version
My name is entropy_narcissist.exe

The Entropy of myself is 6.142286625408597

LINUX version
My name is entropy_narcissist

The Entropy of myself is 5.450343613062795```

## Go

```package main

import (
"fmt"
"io/ioutil"
"log"
"math"
"os"
"runtime"
)

func main() {
_, src, _, _ := runtime.Caller(0)
fmt.Println("Source file entropy:", entropy(src))
fmt.Println("Binary file entropy:", entropy(os.Args[0]))
}

func entropy(file string) float64 {
if err != nil {
log.Fatal(err)
}
var f [256]float64
for _, b := range d {
f[b]++
}
hm := 0.
for _, c := range f {
if c > 0 {
hm += c * math.Log2(c)
}
}
l := float64(len(d))
return math.Log2(l) - hm/l
}
```
Output:
```Source file entropy: 5.038501725029859
Binary file entropy: 5.388171194771937
```

```import qualified Data.ByteString as BS
import Data.List
import System.Environment

(>>>) = flip (.)

main = getArgs >>= head >>> BS.readFile >>= BS.unpack >>> entropy >>> print

entropy = sort >>> group >>> map genericLength >>> normalize >>> map lg >>> sum
where lg c = -c * logBase 2 c
normalize c = let sc = sum c in map (/ sc) c
```
Output:

In a shell

```\$ ghc --make -O3 Narcissist.hs
```

Entropy of the source

```\$ ./Narcissist Narcissist.hs
4.452645183154108
```

Entropy of the binary

```\$ ./Narcissist Narcissist
5.525417236346172
```

## J

Solution:

```   entropy=:  +/@:-@(* 2&^.)@(#/.~ % #)
1!:2&2 entropy 1!:1 (4!:4 <'entropy') { 4!:3''
```

Example:

```   load 'entropy.ijs'
4.73307
```

## Java

```import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class EntropyNarcissist {

private static final String FILE_NAME = "src/EntropyNarcissist.java";

public static void main(String[] args) {
System.out.printf("Entropy of file \"%s\" = %.12f.%n", FILE_NAME, getEntropy(FILE_NAME));
}

private static double getEntropy(String fileName) {
Map<Character,Integer> characterCount = new HashMap<>();
int length = 0;

int c = 0;
characterCount.merge((char) c, 1, (v1, v2) -> v1 + v2);
length++;
}
}
catch ( IOException e ) {
throw new RuntimeException(e);
}

double entropy = 0;
for ( char key : characterCount.keySet() ) {
double fraction = (double) characterCount.get(key) / length;
entropy -= fraction * Math.log(fraction);
}

return entropy / Math.log(2);
}

}
```
Output:
`Entropy of file "src/EntropyNarcissist.java" = 4.691381977073.`

## jq

Works with jq, the C implementation of jq

Works with gojq, the Go implementation of jq

Works with jaq, the Rust implementation of jq

The program assumes it will be presented to itself using an invocation of jq with the -sR options, along the lines of:

```jq -sR -f entropy-narcissist.jq < entropy-narcissist.jq
```

If your jq supports `keys_unsorted`, feel free to use it instead of `keys`.

```def chars: explode[] | [.] | implode;

def bow(stream):
reduce stream as \$word ({}; .[(\$word|tostring)] += 1);

def sum(s): reduce s as \$x (0; .+\$x);

length as \$l
| bow(chars)
| sum(keys[] as \$k | .[\$k] as \$c | \$c * (\$c|log2) )
| (\$l|log2) - ./\$l```
Output:
```{{output}}
<pre>
4.796499915496963
```

## Julia

```using DataStructures

entropy(s) = -sum(x -> x / length(s) * log2(x / length(s)), values(counter(s)))
```
Output:
`self-entropy: 4.716527560525572`

## Kotlin

```// version 1.1.0 (entropy_narc.kt)

fun log2(d: Double) = Math.log(d) / Math.log(2.0)

fun shannon(s: String): Double {
val counters = mutableMapOf<Char, Int>()
for (c in s) {
if (counters.containsKey(c)) counters[c] = counters[c]!! + 1
else counters.put(c, 1)
}
val nn = s.length.toDouble()
var sum = 0.0
for (key in counters.keys) {
val term = counters[key]!! / nn
sum += term * log2(term)
}
return -sum
}

fun main(args: Array<String>) {
println("This program's entropy is \${"%18.16f".format(shannon(prog))}")
}
```
Output:
```This program's entropy is 4.8471803665906705
```

## Lua

arg[0] gives the path of the script currently being executed

```function getFile (filename)
local inFile = io.open(filename, "r")
inFile:close()
return fileContent
end

function log2 (x) return math.log(x) / math.log(2) end

function entropy (X)
local N, count, sum, i = X:len(), {}, 0
for char = 1, N do
i = X:sub(char, char)
if count[i] then
count[i] = count[i] + 1
else
count[i] = 1
end
end
for n_i, count_i in pairs(count) do
sum = sum + count_i / N * log2(count_i / N)
end
return -sum
end

print(entropy(getFile(arg[0])))
```
Output:
`4.3591214356783`

## Nim

As we have compiled without specific options to change the way the executable is named, we can retrieve the source file name by adding the suffix “.nim” to the executable file name. We suppose also that the source file is in the same directory as the executable (which is true in our environment).

```import os, math, strutils, tables

let execName = getAppFilename().splitPath().tail
let srcName = execName & ".nim"

func entropy(str: string): float =
var counts: CountTable[char]
for ch in str:
counts.inc(ch)
for count in counts.values:
result -= count / str.len * log2(count / str.len)

echo "Source file entropy: ", srcName.readFile().entropy().formatFloat(ffDecimal, 5)
echo "Binary file entropy: ", execName.readFile().entropy().formatFloat(ffDecimal, 5)
```
Output:
```Source file entropy: 4.75555
Binary file entropy: 5.97036```

## PARI/GP

```entropy(s)=s=Vec(s);my(v=vecsort(s,,8));-sum(i=1,#v,(x->x*log(x))(sum(j=1,#s,v[i]==s[j])/#s))/log(2);
entropy(Str(entropy))```
Output:
`%1 = 4.54978213`

## Perl

```#!/usr/bin/perl
use strict ;
use warnings ;
use feature 'say' ;

sub log2 {
my \$number = shift ;
return log( \$number ) / log( 2 ) ;
}

open my \$fh , "<" , \$ARGV[ 0 ] or die "Can't open \$ARGV[ 0 ]\$!\n" ;
my %frequencies ;
my \$totallength = 0 ;
while ( my \$line = <\$fh> ) {
chomp \$line ;
next if \$line =~ /^\$/ ;
map { \$frequencies{ \$_ }++ } split( // , \$line ) ;
\$totallength += length ( \$line ) ;
}
close \$fh ;
my \$infocontent = 0 ;
for my \$letter ( keys %frequencies ) {
my \$content = \$frequencies{ \$letter } / \$totallength ;
\$infocontent += \$content * log2( \$content ) ;
}
\$infocontent *= -1 ;
say "The information content of the source file is \$infocontent !" ;
```
Output:
`The information content of the source file is 4.6487923749222 !`

## Phix

Minor edit to the Entropy answer, if compiled assumes source code is in the same directory.

```without js -- command_line, file i/o
function entropy(sequence s)
sequence symbols = {},
counts = {}
integer N = length(s)
for i=1 to N do
object si = s[i]
integer k = find(si,symbols)
if k=0 then
symbols = append(symbols,si)
counts = append(counts,1)
else
counts[k] += 1
end if
end for
atom H = 0
for i=1 to length(counts) do
atom ci = counts[i]/N
H -= ci*log2(ci)
end for
return H
end function

?entropy(get_text(open(substitute(command_line()[2],".exe",".exw")),"rb"))
```

Output is eg 4.993666233, but that may vary with Windows/Linux line endings, tabs vs spaces, trailing returns, BOM headers, etc.

## PHP

```<?php
\$h  =                             0;
\$s  =   file_get_contents(__FILE__);
\$l  =                    strlen(\$s);
foreach ( count_chars(\$s, 1) as \$c )
\$h -=
( \$c / \$l ) *
log( \$c / \$l, 2 );
echo                             \$h;
```
Output:
`2.9339128173013`

## Picat

Translation of: Go
Works with: Picat
```entropy(File) = E =>
F = [0: I in 1..256],
foreach (B in Bytes)
B1 := B + 1,
F[B1] := F[B1] + 1
end,
HM = 0,
foreach (C in F)
if (C > 0) then
HM := HM + C * log(2, C)
end
end,
L = Bytes.length,
E = log(2, L) - HM / L.

main(Args) =>
printf("Entropy: %f\n", entropy(Args[1])).```
Output:
```\$ picat entropy.pi entropy.pi
Entropy: 4.384622
```

## PicoLisp

```(scl 8)

(setq LN2 0.693147180559945309417)

(setq Me
(let F (file)

(setq Hist NIL Sz 0)
(in Me
(use Ch
(while (setq Ch (rd 1))
(inc 'Sz)
(if (assoc Ch Hist)
(con @ (inc (cdr @)))
(setq Hist (cons (cons Ch 1) Hist))))))

(prinl "My entropy is "
(format
(*/
(sum
'((Pair)
(let R (*/ (cdr Pair) 1. Sz)
(- (*/ R (log R) 1.))))
Hist)
1. LN2)
*Scl))

(bye)```
Output:
```My entropy is 4.12169822
```

## Python

Works with: Python 3.4

Minor edit to the Entropy answer.

```import math
from collections import Counter

def entropy(s):
p, lns = Counter(s), float(len(s))
return -sum( count/lns * math.log(count/lns, 2) for count in p.values())

with open(__file__) as f:

print(entropy(b))
```
Output:
`4.575438063744619`

## Racket

The entropy of the program below is 4.512678555350348.

```#lang racket
(require math)
(define (log2 x) (/ (log x) (log 2)))
(define ds (string->list (file->string "entropy.rkt")))
(define n (length ds))
(- (for/sum ([(d c) (in-hash (samples->hash ds))])
(* (/ c n) (log2 (/ c n)))))
```

## Raku

(formerly Perl 6)

Works with: rakudo version 2016.05
```say log(2) R/ [+] map -> \p { p * -log p }, \$_.comb.Bag.values >>/>> +\$_
given slurp(\$*PROGRAM-NAME).comb
```

Result should be in the neighborhood of 4.9

Output:
`4.89351613053006`

## REXX

REXX doesn't have a BIF (built-in function) for   log   or   ln,   so the subroutine (function)   log2   is included herein.

```/*REXX program calculates the   "information entropy"   for  ~this~  REXX program.      */
numeric digits length( e() ) % 2   -  length(.)  /*use 1/2 of the decimal digits of  E. */
#= 0;   @.= 0;   \$=;   \$\$=;   recs= sourceline() /*define some handy─dandy REXX vars.   */
do m=1  for recs; \$=\$||sourceLine(m) /* [↓]  obtain program source and ──► \$*/
end   /*m*/                          /* [↑]  \$ str won't have any meta chars*/
L=length(\$)                                      /*the byte length of this REXX program.*/
do j=1  for L;  _= substr(\$, j, 1)   /*process each character in  \$  string.*/
if @._==0  then do;  #= # + 1        /*¿Character unique?  Bump char counter*/
\$\$= \$\$ || _     /*add this character to the  \$\$  list. */
end
@._= @._ + 1                         /*keep track of this character's count.*/
end   /*j*/                          /* [↑]  characters are all 8─bit bytes.*/
sum= 0                                           /*calculate info entropy for each char.*/
do i=1  for #;  _= substr(\$\$, i, 1)  /*obtain a character from unique list. */
sum= sum -  @._ / L * log2(@._ / L)  /*add {negatively} the char entropies. */
end   /*i*/
say '    program length: '   L                   /*pgm length doesn't include meta chars*/
say 'program statements: '   recs                /*pgm statements are actually pgm lines*/
say ' unique characters: '   #;           say    /*characters are 8─bit bytes of the pgm*/
say 'The information entropy of this REXX program ──► '       format(sum,,12)
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
e: e= 2.718281828459045235360287471352662497757247093699959574966967627724076630; return e
/*──────────────────────────────────────────────────────────────────────────────────────*/
log2: procedure;  parse arg x 1 ox;     ig= x>1.5;     ii= 0;         is= 1 - 2 * (ig\==1)
numeric digits digits()+5;        call e   /*the precision of E must be≥digits(). */
do  while  ig & ox>1.5 | \ig&ox<.5;       _= e;       do j=-1;   iz= ox * _ ** -is
if j>=0 & (ig & iz<1 | \ig&iz>.5)  then leave;    _= _ * _;    izz= iz;  end /*j*/
ox=izz;  ii=ii+is*2**j;  end /*while*/;   x= x * e** -ii -1;   z= 0;  _= -1;  p= z
do k=1;   _= -_ * x;   z= z+_/k;        if z=p  then leave;  p= z;    end  /*k*/
r= z + ii;  if arg()==2  then return r;   return r / log2(2,.)
```
output   when using this REXX program as input:
```    program length:  2631
program statements:  31
unique characters:  79

The information entropy of this REXX program ──►  4.362691425984
```

## Ruby

```def entropy(s)
counts = s.each_char.tally
size = s.size.to_f
counts.values.reduce(0) do |entropy, count|
freq = count / size
entropy - freq * Math.log2(freq)
end
end

p entropy(s)
```
Output:
```4.653607496799478
```

## Rust

```use std::fs::File;

fn entropy<I: IntoIterator<Item = u8>>(iter: I) -> f32 {
let mut histogram = [0u64; 256];
let mut len = 0u64;

for b in iter {
histogram[b as usize] += 1;
len += 1;
}

histogram
.iter()
.cloned()
.filter(|&h| h > 0)
.map(|h| h as f32 / len as f32)
.map(|ratio| -ratio * ratio.log2())
.sum()
}

fn main() {
let name = std::env::args().nth(0).expect("Could not get program name.");
println!("Entropy is {}.", entropy(file.bytes().flatten()));
}
```
Output:
`Entropy is 5.7108583.`

## Sidef

```func entropy(s) {
[0,
s.chars.freq.values.map {|c|
var f = c/s.len
f * f.log2
}...
]«-»
}

say entropy(File(__FILE__).open_r.slurp)
```
Output:
```4.27307750866434915713432109186549
```

## Tcl

Note that this code doesn't bother to close the open handle on the script; it is only suitable as a demonstration program.

```proc entropy {str} {
set log2 [expr log(2)]
foreach char [split \$str ""] {dict incr counts \$char}
set entropy 0.0
foreach count [dict values \$counts] {
set freq [expr {\$count / double([string length \$str])}]
set entropy [expr {\$entropy - \$freq * log(\$freq)/\$log2}]
}
return \$entropy
}

puts [format "entropy = %.5f" [entropy [read [open [info script]]]]]
```
Output:
```entropy = 4.59099
```

## V (Vlang)

Translation of: Go
```import os
import math

fn main() {
println("Binary file entropy: \${entropy(os.args[0])?}")
}

fn entropy(file string) ?f64 {

mut f := [256]f64{}
for b in d {
f[b]++
}
mut hm := 0.0
for c in f {
if c > 0 {
hm += c * math.log2(c)
}
}
l := f64(d.len)
return math.log2(l) - hm/l
}
```
Output:
```Binary file entropy: 5.676177202237735
```

## Wren

Basically an amalgam of the code in the Print_itself#Wren and Entropy#Wren tasks.

```import "os" for Process
import "io" for File

var args = Process.allArguments
var m = {}
for (c in s) {
var d = m[c]
m[c] = (d) ? d + 1 : 1
}
var hm = 0
for (k in m.keys) {
var c = m[k]
hm = hm + c * c.log2
}
var l = s.count
System.print(l.log2 - hm/l)
```
Output:
```4.6302314663
```

## XPL0

To run: entropy < entropy.xpl

```int  Count(128), I, Len, Ch;
real Sum, Prob;
[for I:= 0 to 127 do Count(I):= 0;
Len:= 0;
loop    [Ch:= ChIn(1);
if Ch = \$1A\EOF\ then quit;
Count(Ch):= Count(Ch)+1;
Len:= Len+1;
];
Sum:= 0.;
for I:= 0 to 127 do
if Count(I) then
[Prob:= float(Count(I)) / float(Len);
Sum:= Sum + Prob*Ln(Prob);
];
RlOut(0, -Sum/Ln(2.));
]```
Output:
`    4.63457`

## zkl

Minor edit to the Entropy answer.

```fcn entropy(text){
text.pump(Void,fcn(c,freq){ c=c.toAsc(); freq[c]=freq[c]+1; freq }
.fp1((0).pump(256,List,(0.0).create.fp(0)).copy()))
.filter()		      // remove all zero entries
.apply('/(text.len()))     // (num of char)/len
.apply(fcn(p){-p*p.log()}) // |p*ln(p)|
.sum(0.0)/(2.0).log();     // sum * ln(e)/ln(2) to convert to log2
}

```4.8422