Selecting some lists from a list of lists












1















I would like to have some lists from a list of lists under a certain condition. For example:



`((a w) (e w))`


from



`((a w) (e w) (i u) (o u))`


where the condition is to have 'w in the second position.



My code



(filter (andmap (equal? (cdr lst) 'w)) 'lst)



with



(define lst '((a w) (e w) (i u) (o u)))



is not working. What am I doing wrong?






scheme nested-lists







share|improve this question























  • Please be more specific than "is not working" when you're describing a problem.

    – molbdnilo
    Nov 19 '18 at 14:41








  • 1





    Start with writing a predicate that works with one list element – that is, a procedure p such that (p '(a w)) is #t and (p '(i u)) is #f. Then use that. (andmap is of no use here.)

    – molbdnilo
    Nov 19 '18 at 14:44


















1















I would like to have some lists from a list of lists under a certain condition. For example:



`((a w) (e w))`


from



`((a w) (e w) (i u) (o u))`


where the condition is to have 'w in the second position.



My code



(filter (andmap (equal? (cdr lst) 'w)) 'lst)



with



(define lst '((a w) (e w) (i u) (o u)))



is not working. What am I doing wrong?






scheme nested-lists







share|improve this question























  • Please be more specific than "is not working" when you're describing a problem.

    – molbdnilo
    Nov 19 '18 at 14:41








  • 1





    Start with writing a predicate that works with one list element – that is, a procedure p such that (p '(a w)) is #t and (p '(i u)) is #f. Then use that. (andmap is of no use here.)

    – molbdnilo
    Nov 19 '18 at 14:44
















1












1








1








I would like to have some lists from a list of lists under a certain condition. For example:



`((a w) (e w))`


from



`((a w) (e w) (i u) (o u))`


where the condition is to have 'w in the second position.



My code



(filter (andmap (equal? (cdr lst) 'w)) 'lst)



with



(define lst '((a w) (e w) (i u) (o u)))



is not working. What am I doing wrong?






scheme nested-lists







share|improve this question














I would like to have some lists from a list of lists under a certain condition. For example:



`((a w) (e w))`


from



`((a w) (e w) (i u) (o u))`


where the condition is to have 'w in the second position.



My code



(filter (andmap (equal? (cdr lst) 'w)) 'lst)



with



(define lst '((a w) (e w) (i u) (o u)))



is not working. What am I doing wrong?






scheme nested-lists




scheme nested-lists






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 19 '18 at 13:04









gibariangibarian

626




626













  • Please be more specific than "is not working" when you're describing a problem.

    – molbdnilo
    Nov 19 '18 at 14:41








  • 1





    Start with writing a predicate that works with one list element – that is, a procedure p such that (p '(a w)) is #t and (p '(i u)) is #f. Then use that. (andmap is of no use here.)

    – molbdnilo
    Nov 19 '18 at 14:44





















  • Please be more specific than "is not working" when you're describing a problem.

    – molbdnilo
    Nov 19 '18 at 14:41








  • 1





    Start with writing a predicate that works with one list element – that is, a procedure p such that (p '(a w)) is #t and (p '(i u)) is #f. Then use that. (andmap is of no use here.)

    – molbdnilo
    Nov 19 '18 at 14:44



















Please be more specific than "is not working" when you're describing a problem.

– molbdnilo
Nov 19 '18 at 14:41







Please be more specific than "is not working" when you're describing a problem.

– molbdnilo
Nov 19 '18 at 14:41






1




1





Start with writing a predicate that works with one list element – that is, a procedure p such that (p '(a w)) is #t and (p '(i u)) is #f. Then use that. (andmap is of no use here.)

– molbdnilo
Nov 19 '18 at 14:44







Start with writing a predicate that works with one list element – that is, a procedure p such that (p '(a w)) is #t and (p '(i u)) is #f. Then use that. (andmap is of no use here.)

– molbdnilo
Nov 19 '18 at 14:44














1 Answer
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You should not quote the list: 'lst is not the same as lst. And to access the second element, use second (if that's not defined, use cadr instead). With cdr you get the rest of the list (which is another list), not its second element. Oh, and filter expects a lambda as its first argument, not andmap. This is what I mean:



(define lst '((a w) (e w) (i u) (o u)))

(filter (lambda (sl) (equal? (second sl) 'w))

        lst)

=> '((a w) (e w))





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    active

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    active

    oldest

    votes









    1














    You should not quote the list: 'lst is not the same as lst. And to access the second element, use second (if that's not defined, use cadr instead). With cdr you get the rest of the list (which is another list), not its second element. Oh, and filter expects a lambda as its first argument, not andmap. This is what I mean:



    (define lst '((a w) (e w) (i u) (o u)))
    
(filter (lambda (sl) (equal? (second sl) 'w))
    
        lst)
    
=> '((a w) (e w))





    share|improve this answer




























      1














      You should not quote the list: 'lst is not the same as lst. And to access the second element, use second (if that's not defined, use cadr instead). With cdr you get the rest of the list (which is another list), not its second element. Oh, and filter expects a lambda as its first argument, not andmap. This is what I mean:



      (define lst '((a w) (e w) (i u) (o u)))
      
(filter (lambda (sl) (equal? (second sl) 'w))
      
        lst)
      
=> '((a w) (e w))





      share|improve this answer


























        1












        1








        1







        You should not quote the list: 'lst is not the same as lst. And to access the second element, use second (if that's not defined, use cadr instead). With cdr you get the rest of the list (which is another list), not its second element. Oh, and filter expects a lambda as its first argument, not andmap. This is what I mean:



        (define lst '((a w) (e w) (i u) (o u)))
        
(filter (lambda (sl) (equal? (second sl) 'w))
        
        lst)
        
=> '((a w) (e w))





        share|improve this answer













        You should not quote the list: 'lst is not the same as lst. And to access the second element, use second (if that's not defined, use cadr instead). With cdr you get the rest of the list (which is another list), not its second element. Oh, and filter expects a lambda as its first argument, not andmap. This is what I mean:



        (define lst '((a w) (e w) (i u) (o u)))
        
(filter (lambda (sl) (equal? (second sl) 'w))
        
        lst)
        
=> '((a w) (e w))






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 19 '18 at 15:42









        Óscar LópezÓscar López

        176k24225321




        176k24225321






























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