Matrix2 does not support OrderedSerialization.

[johnynek]

Ofter Orderings are composed in here:

https://github.com/twitter/scalding/blob/develop/scalding-core/src/main/scala/com/twitter/scalding/mathematics/Matrix2.scala

We need to do that using:
https://github.com/twitter/scalding/blob/develop/scalding-serialization/src/main/scala/com/twitter/scalding/serialization/Serialization2.scala#L61

if all Orderings are OrderedSerializations. We probably need some method like:

implicit def withOrderedSerialization[A: Ordering, B: Ordering]: Ordering[(A, B)] =
  // if both Orderings are OrderedSerialization, use OrderedSerialization2, else Ordering.tuple2 

and use that in internal methods.

[reconditesea]

@johnynek Here I think if the individual ordering for row/col is an OrderedSerialization, it will just work. But for the composed ordering of the two, we will need to add OrderedSerialization support. Is this correct?

[johnynek]

Yes, that's right. Sometimes we group on the pair, and that needs to be composed properly.