Question

Let’s say that I have a List (or the values in a Map), and i want to perform an operation on each item. But unfortunately, for whatever reason, this list of values can contain nulls.

scala> val players = List("Messi", null, "Xavi", "Iniesta", null)
players: List[java.lang.String] = List(Messi, null, Xavi, Iniesta, null)

In order to avoid blowing up with a NPE, i need to do the following:

scala> players.filterNot(_ == null ).map(_.toUpperCase)
res84: List[java.lang.String] = List(MESSI, XAVI, INIESTA)

Is there any better way of doing this?

Ideally something like:

players.safeMap(_.toUpperCase)

On the scala-language mailing list, Simon proposed this:

players.filter ( null !=).map(_.toUpperCase )

which is shorter version of my original take, and as short as you can get without a dedicated method.

Even better, Stefan and Kevin proposed the method withFilter which will return a lazy proxy, so both operations can be merged.

players.withFilter ( null !=).map(_.toUpperCase )

Answer 1

If you can’t avoid nulls (e.g. if you get your list from Java code), another alternative is to use collect instead of map:

scala> players.collect { case player if player != null => player.toUpperCase }
res0: List[java.lang.String] = List(MESSI, XAVI, INIESTA)