map a function over a list of lists and concatenates the result into a list

Question

How can I map a function for instance (square x) over a list of lists (list (list 1 2) (list 3 4)) and at the same time concatenates the result. For example the result would be (1 4 9 16). I can't find any detailed explanations on the web... thanks for any advice!

Best Regards, Eunice

https://stackoverflow.com/questions/14617095/how-to-use-append-map-in-racket-scheme#14617333 — Jeffrey Chung, May 30 '17 at 15:16
Possible duplicate of [How to use append-map in Racket (Scheme)](https://stackoverflow.com/questions/14617095/how-to-use-append-map-in-racket-scheme) — Shiro, May 30 '17 at 16:22

score 2 · Accepted Answer · answered May 30 '17 at 15:41

Try this:

(append-map (lambda (slst) (map sqr slst))
            (list (list 1 2) (list 3 4)))

The innermost map squares each number, and the outermost append-map traverses the sublists, appending them at the end. In case your language doesn't support append-map, here's an equivalent solution:

(apply append
       (map (lambda (slst) (map sqr slst))
            (list (list 1 2) (list 3 4))))

map a function over a list of lists and concatenates the result into a list

1 Answers1