Tricky scala collections

gistfile1.scala

// Beware of iterating/yielding over multiple collections with a Set in the middle.
// Due to Scala's desire to keep intermediate type, you'll inadvertantly remove 
// duplicates from the inner collection. This may or may not be desirable depending
// on your use case.

// Note Set in the middle. This yields the correct value because the last collection has no duplicates.
scala> for (a <- List(1); b <- Set(1); c <- List(1,2)) yield (a,c)
res6: List[(Int, Int)] = List((1,1), (1,2))

// Note the Set in the middle. This gets rid of duplicates in List(1,1) due to the Set before it! This may or may not
// be desirable.
scala> for (a <- List(1); b <- Set(1); c <- List(1,1)) yield (a,c)
res7: List[(Int, Int)] = List((1,1))

// Note that we changed the middle collection from Set to Seq. This does not get rid of duplicates.
scala> for (a <- List(1); b <- Seq(1); c <- List(1,1)) yield (a,c)
res8: List[(Int, Int)] = List((1,1), (1,1))