Selecting some lists from a list of lists
up vote
1
down vote
favorite
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 at 13:04
gibarian
365
add a comment |
up vote
1
down vote
favorite
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 at 13:04
gibarian
365
Please be more specific than "is not working" when you're describing a problem.
– molbdnilo
Nov 19 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 at 14:44
add a comment |
up vote
1
down vote
favorite
up vote
1
down vote
favorite
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 at 13:04
gibarian
365
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 at 13:04
gibarian
365
asked Nov 19 at 13:04
gibarian
365
asked Nov 19 at 13:04
gibarian
365
asked Nov 19 at 13:04
gibarian
365
asked Nov 19 at 13:04
gibarian
365
365
Please be more specific than "is not working" when you're describing a problem.
– molbdnilo
Nov 19 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 at 14:44
add a comment |
Please be more specific than "is not working" when you're describing a problem.
– molbdnilo
Nov 19 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 at 14:44
Please be more specific than "is not working" when you're describing a problem.
– molbdnilo
Nov 19 at 14:41
Please be more specific than "is not working" when you're describing a problem.
– molbdnilo
Nov 19 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 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 at 14:44
add a comment |
1 Answer
1
active
oldest
votes
up vote
1
down vote
accepted
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 at 15:42
Óscar López
174k22224319
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
1
down vote
accepted
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 at 15:42
Óscar López
174k22224319
add a comment |
up vote
1
down vote
accepted
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 at 15:42
Óscar López
174k22224319
add a comment |
up vote
1
down vote
accepted
up vote
1
down vote
accepted
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 at 15:42
Óscar López
174k22224319
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 at 15:42
Óscar López
174k22224319
answered Nov 19 at 15:42
Óscar López
174k22224319
answered Nov 19 at 15:42
Óscar López
174k22224319
answered Nov 19 at 15:42
Óscar López
174k22224319
174k22224319
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 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 at 14:44