One of the useful features of ess-mode (Emacs speaks statistics) is to automatically replace the underscore _ with the assignment operator <-. Lately, I have been using a lot of pipes (written as %>%) and it would be great to not have to type three characters for each pipe.
Is it possible to define a custom key binding for the pipe, similar to the one converting _ into ->?
The simplest solution is to just bind a key to insert a string:
(define-key ess-mode-map (kbd "|") "%>%")
You can still insert | with C-q |. I'm not sure about the map's name; you'll almost certainly want to limit the key binding to ess-mode.