24 lines
807 B
Racket
24 lines
807 B
Racket
#lang racket
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(require math)
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(provide entropy hash-entropy list-entropy digital-entropy)
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(define (hash-entropy h)
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(define (log2 x) (/ (log x) (log 2)))
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(define n (for/sum [(c (in-hash-values h))] c))
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(- (for/sum ([c (in-hash-values h)] #:unless (zero? c))
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(* (/ c n) (log2 (/ c n))))))
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(define (list-entropy x) (hash-entropy (samples->hash x)))
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(define entropy (compose list-entropy string->list))
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(define digital-entropy (compose entropy number->string))
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(module+ test
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(require rackunit)
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(check-= (entropy "1223334444") 1.8464393446710154 1E-8)
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(check-= (digital-entropy 1223334444) (entropy "1223334444") 1E-8)
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(check-= (digital-entropy 1223334444) 1.8464393446710154 1E-8)
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(check-= (entropy "xggooopppp") 1.8464393446710154 1E-8))
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(module+ main (entropy "1223334444"))
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