Selecting some lists from a list of lists
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
asked Nov 19 '18 at 13:04
gibariangibarian
626
add a comment |
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
asked Nov 19 '18 at 13:04
gibariangibarian
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 procedurepsuch that(p '(a w))is#tand(p '(i u))is#f. Then use that. (andmapis of no use here.)
– molbdnilo
Nov 19 '18 at 14:44
add a comment |
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
asked Nov 19 '18 at 13:04
gibariangibarian
626
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
asked Nov 19 '18 at 13:04
gibariangibarian
626
asked Nov 19 '18 at 13:04
gibariangibarian
626
asked Nov 19 '18 at 13:04
gibariangibarian
626
asked Nov 19 '18 at 13:04
gibariangibarian
626
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 procedurepsuch that(p '(a w))is#tand(p '(i u))is#f. Then use that. (andmapis of no use here.)
– molbdnilo
Nov 19 '18 at 14:44
add a comment |
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 procedurepsuch that(p '(a w))is#tand(p '(i u))is#f. Then use that. (andmapis 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
add a comment |
1 Answer
1
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oldest
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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))
answered Nov 19 '18 at 15:42
Óscar LópezÓscar López
178k25227323
add a comment |
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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))
answered Nov 19 '18 at 15:42
Óscar LópezÓscar López
178k25227323
add a comment |
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))
answered Nov 19 '18 at 15:42
Óscar LópezÓscar López
178k25227323
add a comment |
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))
answered Nov 19 '18 at 15:42
Óscar LópezÓscar López
178k25227323
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))
answered Nov 19 '18 at 15:42
Óscar LópezÓscar López
178k25227323
answered Nov 19 '18 at 15:42
Óscar LópezÓscar López
178k25227323
answered Nov 19 '18 at 15:42
Óscar LópezÓscar López
178k25227323
answered Nov 19 '18 at 15:42
Óscar LópezÓscar López
178k25227323
178k25227323
add a comment |
add a comment |
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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
psuch that(p '(a w))is#tand(p '(i u))is#f. Then use that. (andmapis of no use here.)– molbdnilo
Nov 19 '18 at 14:44