Doing people's homework are we?
On 5/17/2017 8:08 PM, Matthew Butterick wrote:
`slice-at`
http://docs.racket-lang.org/sugar/index.html?q=slice-at#%28def._%28%28lib._sugar%2Flist..rkt%29._slice-at%29%29
<http://docs.racket-lang.org/sugar/index.html?q=slice-at#%28def._%28%28lib._sugar/list..rkt%29._slice-at%29%29>
On May 17, 2017, at 3:56 PM, Don Green <infodeveloper...@gmail.com
<mailto:infodeveloper...@gmail.com>> wrote:
Racket code that could perform this list manipulation?
(every-n-lists-into-list <n-lists-to-group> '(<in-list>))
(every-n-lists-into-list 1 '((1) (2))) ;=> '(((1) (2)))
(every-n-lists-into-list 2 '((1) (2) (3) (4))) ;=> '(((1) (2)) ((3) (4)))
(every-n-lists-into-list 3 '((1) (2) (3) (4)) (5) (6))) ;=> '(((1)
(2) (3)) ((4) (5) (6)))
Very nice! Unfortunately, the existence of sugar was unknown to me
until just now. More evidence that one can spend a lifetime learning
what batteries Racket already has included.
My 1st thought was to use split-at:
#lang racket
(define (group-items n items)
;; check # of items
(unless (= 0 (modulo (length items) n))
(error "not enough items"))
;; split and reassemble
(let loop [
(items items)
(result '())
]
(if [null? items]
(reverse result)
(let-values [((head tail)(split-at items n))]
(loop tail (cons head result)))
))
)
George
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