CODEWITHSUNDEEP
racket
codegirl
codegirl

Reputation: 1

Parsing through a list in racket

Given a list define: 

(define list
 '((a1 20 (1 a2) (3 a3))
  (a2 10 (2 a4))
  (a3 10 (1 a5) (2 a6) (3 a7))
  (a4 21)
  (a5 12)
  (a6 6 (1 a4) (2 a5))

) )

How do you write a function (sub 'a1) would return a list (a2 a3). I can find the list ((1 a2) (3 a3)) with the following code:

(define (sub val)
 (cdr(cdr(cond ((assq val list))
        (else 0)))))

But what do I do after that to get only the elements I want? I tried doing some recursion but that just lead in circles. Any advice would be appreciated.

Second question: a function to get a list of only "a" with a number value less than or equal to given input i.e (test 10) would return (a2 a3 a6) I can check one a list but I'm stuck at how to go through all the list of list and append the values.

Upvotes: 0

Views: 423

Answers (1)

fanton
fanton

Reputation: 720

All you need is the map function. So, either use your own sub function like this:

(map cadr (sub 'a1))

Or change your function to include the map:

(define (sub val)
    (map cadr (cdr(cdr(cond ((assq val list))
        (else 0))))))

(cadr lst) is just a shortcut for (car (cdr lst)). My Racket skills are a bit rusty, so I will refrain from saying that your sub function is entirely correct or has any glitches.

Upvotes: 0

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