Entropy/Narcissist

Entropy/Narcissist is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Write a program that computes and shows its own entropy.

J

Solution:<lang j> entropy=: +/@:-@(* 2&^.)@(#/.~ % #)

  1!:2&2 entropy 1!:1 (4!:4 <'entropy') { 4!:3</lang>

Example:<lang j> load 'entropy.ijs' 4.73307</lang>

Perl 6

<lang Perl 6>say log(2) R/ [+] map -> \p { p * -log p }, $_.bag.values »/» +$_

   given slurp($*PROGRAM_NAME).comb</lang>

Output:

4.98893170929151

Tcl

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

Output:

entropy = 4.59099