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75 lines
1.9 KiB
Scheme
75 lines
1.9 KiB
Scheme
(define-module (deliberate utils)
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#:use-module (srfi srfi-1)
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#:export (const-list range reorder string-count zip))o
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(define (const-list length value)
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(if (= length 0)
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'()
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(cons value (const-list (- length 1) value))))
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;; Return a list of integers in the half-open interval [low, high)
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(define (range low high)
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(if (eq? low high)
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'()
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(cons low (range (+ 1 low) high))))
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;; Combine lists component-wise
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;; Similar to python zip()
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;;
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;; Parameters:
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;; args: Any number of lists
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;;
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;; Returns:
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;; A list. The nth element is a list of the
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;; nth elements of each argument
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;;
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(define (zip . args)
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(if (or (nil? args) (memq '() args))
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'()
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(cons (map car args)
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(apply zip (map cdr args)))))
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;; Reorder one list by another
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;; A reordering is applied to lst such that the same reordering would
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;; Put rank in asending oder.
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;;
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;; Parameters:
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;; lst: The list to reorder
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;; ranks: The list to sort by
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;;
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;; Returns:
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;; A reordered copy of lst
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;;
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(define (reorder lst ranks)
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(let* ((pairs (zip lst ranks))
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(ranked-pairs
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(filter (lambda (pair) (not (eq? #f (cadr pair))))
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pairs))
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(sorted-pairs
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(sort ranked-pairs (lambda (a b) (< (cadr a) (cadr b))))))
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(map car sorted-pairs)))
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;; Same as string-count but assumes parameter is sorted
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(define (string-count-sorted sorted)
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(if (nil? sorted)
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'()
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(let* ((elt (car sorted))
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(total-length (length sorted))
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(rest (find-tail (lambda (x) (not (equal? x elt))) sorted))
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(rest-length (if rest (length rest) 0)))
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(cons (cons elt (- total-length rest-length))
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(string-count-sorted rest)))))
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;; Counts the number of times each string appears in a list
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;;
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;; Parameters:
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;; values: The list
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;;
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;; Returns:
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;; An alist of the form ((string1 . count1) ...)
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;;
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(define (string-count values)
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(let ((sorted (sort values string<)))
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(string-count-sorted sorted)))
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