Entropy/Narcissist

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< Entropy(Redirected from Entropy/Narcissic)
Task
Entropy/Narcissist
You are encouraged to solve this task according to the task description, using any language you may know.
ENTROPY.JPG
Task

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


Related Tasks



Ada[edit]

with Ada.Text_Io;
with Ada.Command_Line;
with Ada.Numerics.Elementary_Functions;

procedure Entropy is
   use Ada.Text_Io;

   type Hist_Type is array (Character) of Natural;

   function Log_2 (V : Float) return Float is
      use Ada.Numerics.Elementary_Functions;
   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);
   end Read_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;

   Read_File (Name, Hist);
   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[edit]

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[edit]

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[edit]

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

C[edit]

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++[edit]

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

using namespace std;

string readFile (string path) {
    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 () {
    cout<<entropy(readFile("entropy.cpp"));
    return 0;
}
Output:
4.58688

Crystal[edit]

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

puts entropy File.read(__FILE__)
Output:
4.963709090807145

D[edit]

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

    auto data = sort(cast(ubyte[])args[0].read);
    return data
           .group
           .map!(g => g[1] / double(data.length))
           .map!(p => -p * p.log2)
           .sum
           .writeln;
}
Output:
6.29803

Elixir[edit]

File.open(__ENV__.file, [:read], fn(file) ->
  text = IO.read(file, :all)
  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[edit]

(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[edit]

#! /usr/bin/escript

-define(LOG2E, 1.44269504088896340735992).

main(_) ->
    Self = escript:script_name(),
    {ok, Contents} = file:read_file(Self),
    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[edit]

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 .
] with-file-reader
Output:
4.591946214804276

FreeBASIC[edit]

' 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[edit]

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 {
    d, err := ioutil.ReadFile(file)
    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

Haskell[edit]

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[edit]

Solution:
   entropy=:  +/@:-@(* 2&^.)@(#/.~ % #)
   1!:2&2 entropy 1!:1 (4!:4 <'entropy') { 4!:3''
Example:
   load 'entropy.ijs'
4.73307

Java[edit]

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
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;

        try (BufferedReader reader = new BufferedReader(new FileReader(new File(fileName)));) {        
            int c = 0;
            while ( (c = reader.read()) != -1 ) {
                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.

Julia[edit]

using DataStructures

entropy(s) = -sum(x -> x / length(s) * log2(x / length(s)), values(counter(s)))
println("self-entropy: ", entropy(read(Base.source_path(), String)))
Output:
self-entropy: 4.716527560525572

Kotlin[edit]

// 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>) {
   val prog = java.io.File("entropy_narc.kt").readText()
   println("This program's entropy is ${"%18.16f".format(shannon(prog))}")
}
Output:
This program's entropy is 4.8471803665906705

Lua[edit]

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

function getFile (filename)
    local inFile = io.open(filename, "r")
    local fileContent = inFile:read("*all")
    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[edit]

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[edit]

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[edit]

#!/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[edit]

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[edit]

<?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[edit]

Translation of: Go
Works with: Picat
entropy(File) = E =>
    Bytes = read_file_bytes(File),
    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[edit]

(scl 8)
(load "@lib/math.l")

(setq LN2 0.693147180559945309417)

(setq Me
   (let F (file)
      (pack (car F) (cadr F))))

(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[edit]

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:
    b=f.read()
    
print(entropy(b))
Output:
4.575438063744619

Racket[edit]

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[edit]

(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[edit]

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[edit]

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

s = File.read(__FILE__)
p entropy(s)
Output:
4.653607496799478

Rust[edit]

use std::fs::File;
use std::io::{Read, BufReader};

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.");
    let file = BufReader::new(File::open(name).expect("Could not read file."));
    println!("Entropy is {}.", entropy(file.bytes().flatten()));
}
Output:
Entropy is 5.7108583.

Sidef[edit]

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[edit]

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)[edit]

Translation of: Go
import os
import math

fn main() {
    println("Binary file entropy: ${entropy(os.args[0])?}")
}
 
fn entropy(file string) ?f64 {
    d := os.read_bytes(file)?

    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[edit]

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 s = File.read(args[1]).trim()
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

zkl[edit]

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
}

entropy(File("entropy.zkl").read().text).println();
Output:
4.8422