min/max of collections containing NaN (handling incomparability in ordering)

Question

I just ran into a nasty bug as a result of the following behavior:

scala> List(1.0, 2.0, 3.0, Double.NaN).min
res1: Double = NaN

scala> List(1.0, 2.0, 3.0         


        

Answer 1

For

val a = List(1.0, 2.0, 3.0, Double.NaN)

sort it,

a.sortWith {_ >_ }
res: List[Double] = List(3.0, 2.0, 1.0, NaN)

and so NaN values are relegated, thus for max,

a.sortWith {_ >_ }.head
res: Double = 3.0

Likewise

a.sortWith {_ < _ }
res: List[Double] = List(1.0, 2.0, 3.0, NaN)

and so for min,

a.sortWith {_ < _ }.head
res: Double = 1.0