Well, it's really not too bad.
@new_array_us = ProjectAssignment.find(@new_array_ids). sort_by {|pa| @new_array_ids.index(pa.id)}
(which I'd have put on a single line if it weren't for the inevitable line-wrapping in the email)
In fact, if you didn't want to sort the results, you could have skipped the mapping .to_i since ActiveRecord will treat .find("3") and .find(3) the same.
You can even simplify that bit using Symbol#to_proc
@new_array_ids = params[@resource_key].map(&:to_i)
Enjoy!
-Rob
Rob Biedenharn http://agileconsultingllc.com Rob@AgileConsultingLLC.com