lastIndexOf in CJam

Question

For the question Find the highest unique digit , here is my answer :

9A,sqfe=W%X#-

At the end I am essentially trying to achieve a lastIndexOf. I do that by reversing my array, using indexOf, and subtracting from 9. This adds 4 (9 W % -) extra bytes to get from indexOf to lastIndexOf.

Furthermore, if I didn't know my array was length 10 the code would be even longer, and secondly, this code returns 10 when indexOf is -1 which may not be acceptable in many situations.

Any suggestions on a shorter way to do the lastIndexOf operation (generally or just as needed for this challenge)?

Answer 1

Splitting is sometimes a good way to do this. E.g.

e# Stack: ... haystack needle
a/);S*,

With variants, such as removing the a if both needle and haystack are strings.

Answer 2

9 bytes

_,(@@W%#-

Try it online!

You must have ...element list exactly like this in the stack. If W doesn't contain -1 you must replace it with something that does evaluate to -1.