30 lines
880 B
Racket
30 lines
880 B
Racket
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#lang racket
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(define ht (hash "apple" 'red "banana" 'yellow))
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(module+ test
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(require rackunit)
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(check-equal? (hash-ref ht "apple") 'red))
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(define ht2 (hash-set ht "coconut" 'brown))
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(module+ test
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(check-equal? (hash-ref ht2 "coconut") 'brown)
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(check-exn exn:fail? (lambda () (hash-ref ht "coconut"))))
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(define (census . lst)
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(define (helper lst acc-hash)
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(cond
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[(empty? lst) (hash->list acc-hash)]
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[else
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(let* ([key (first lst)]
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[current (hash-ref acc-hash key 0)])
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(helper (rest lst) (hash-set acc-hash key (add1 current))))]))
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(helper lst (hash)))
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(module+ test
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(check-equal?
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(sort (census 1 2 3 1 2) #:key car <) '((1 . 2) (2 . 2) (3 . 1)))
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(check-equal?
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(sort (census "aardvark" "dingo" "buffalo" "buffalo" "bear") #:key car string<?)
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'(("aardvark" . 1) ("bear" . 1) ("buffalo" . 2) ("dingo" . 1))))
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