replacing a line in a list

I have a list formatted like this:

(list foo '(("q" "2" "3" "4")("w" "2" "3" "4")("e" "2" "3" "4")("r" "2" "3"
"4")))

I want to replace one sub list based on the first item in the list. For
example I have a new list ("z" "2" "3" "4") and I want to replace ("e" "2"
"3" "4") with the new data in the same location to end up with this:

(("q" "2" "3" "4")("w" "2" "3" "4")("z" "2" "3" "4")("r" "2" "3" "4"))

Can someone tell me the logic to do this? I'm thinking it will require the
use of ASSOC and CONS but there is probably a lot more to it than that. Also
I'd prefer basic instructions over raw code so I can try to figure it all
out. Thanks!

kemp

 

(subst <new> <old> <list>)
--

AUTODESK
Authorized Developer
http://www.Cadentity.com
MASi

 

(setq foo '(("q" "2" "3" "4")("w" "2" "3" "4")("e" "2" "3" "4")("r" "2" "3"
"4"))) ;; corrected

(setq foo (subst '("z" "2" "3" "4") '("e" "2" "3" "4") foo)) ;; substituted

-PG.

 

subst is exactly what I needed. Thanks to both of you Doug and Rudy! It
works now

kemp