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Ingy döt Net 2013-10-27 22:24:23 +00:00
parent 6f050a029e
commit 776bba907c
3887 changed files with 59894 additions and 7280 deletions
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28
Task/Entropy/Racket/entropy.rkt
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@ -1,17 +1,23 @@
#lang racket
(require math)
(provide entropy hash-entropy list-entropy digital-entropy)
(define (log2 x)
(/ (log x) (log 2)))
(define (hash-entropy h)
(define (log2 x) (/ (log x) (log 2)))
(define n (for/sum [(c (in-hash-values h))] c))
(- (for/sum ([c (in-hash-values h)] #:unless (zero? c))
(* (/ c n) (log2 (/ c n))))))
(define (digits x)
(for/list ([c (number->string x)])
(- (char->integer c) (char->integer #\0))))
(define (list-entropy x) (hash-entropy (samples->hash x)))
(define (entropy x)
(define ds (digits x))
(define n (length ds))
(- (for/sum ([(d c) (in-hash (samples->hash ds))])
(* (/ d n) (log2 (/ d n))))))
(define entropy (compose list-entropy string->list))
(define digital-entropy (compose entropy number->string))
(entropy 1223334444)
(module+ test
(require rackunit)
(check-= (entropy "1223334444") 1.8464393446710154 1E-8)
(check-= (digital-entropy 1223334444) (entropy "1223334444") 1E-8)
(check-= (digital-entropy 1223334444) 1.8464393446710154 1E-8)
(check-= (entropy "xggooopppp") 1.8464393446710154 1E-8))
(module+ main (entropy "1223334444"))