If I had a N lists each of length M, how could I write a nice clean function to return a single list of length M, where each element is the sum of the corresponding elements in the N lists?
(starting to learn lisp - go easy!)
+8
A:
This is a job for the map and apply functions. Here is a way to do it, with an EDIT suggested by Nathan Sanders:
(define (add-lists . more)
(apply map + more))
Pillsy
2010-03-15 15:33:37
Apply takes multiple arguments, only the last is a list, so you could get away with `(apply map + more)`
Nathan Sanders
2010-03-15 17:58:14
Sorry - I was making some embarrassing mistakes. Thanks for your excellent answer!
ntimes
2010-03-15 18:21:22
@Nathan: Cool. I didn't know that applied to Scheme's `apply`; I do most of my Lisping in CL.
Pillsy
2010-03-15 19:48:21
+2
A:
For a more matlab like syntax:
(define (piecewise func)
(lambda more
(apply map func more)))
(define pw piecewise)
((pw +) '(1 2 3 4 5) '(6 7 8 9 0))
((pw -) '(1 2 3 4 5) '(6 7 8 9 0))
((pw *) '(1 2 3 4 5) '(6 7 8 9 0))
((pw /) '(1 2 3 4 5) '(6 7 8 9 0.1))
outputs:
(7 9 11 13 5)
(-5 -5 -5 -5 5)
(6 14 24 36 0)
(1/6 2/7 3/8 4/9 50.0)
Davorak
2010-03-18 16:12:07
+2
A:
Just this works in MIT scheme.
(map + '(1 2 3) '(4 5 6) '(7 8 9))
;Value 28: (12 15 18)
Fakrudeen
2010-03-19 06:20:30