Sorry, a couple of other small things:

* Instead of doing `itr.map({ case (x, y) => ... })`, you can just do `itr.map { case (x, y) => ... }` without the parens
* There seems to be a line with a tab above -- change it to spaces
* In `mapPartitions {itr =>`, change it to `mapPartitions { itr =>` (with a space after the brace)

Just mentioning these so you can match the style of the rest of the project later.