15 lines
516 B
Racket
15 lines
516 B
Racket
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#lang typed/racket
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(: sum (-> (Listof Number) Number))
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(define (sum list) (foldr + 0 list))
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(: mean (-> (Listof Number) Number))
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(define (mean sample)
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(/ (sum sample) (length sample)))
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(: standard-deviation (-> (Listof Number) Number))
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(define (standard-deviation sample)
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(let* ((degrees-of-freedom (- (length sample) 1))
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(sample-mean (mean sample))
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(sum-of-squared-errors (sum (map (lambda (xi) (expt (- xi sample-mean) 2)) sample))))
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(sqrt (/ sum-of-squared-errors degrees-of-freedom))))
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