How to convert DateTimeComparator to an Ordering[DateTime] in Scala

Question

I just typed this which seems a little ugly:

val maxTime = times.max(DateTimeComparator.getInstance().asInstanceOf[Comparator[DateTime]] asScala)

times is a sequence of org.joda.time.DateTime.

There must be a better way to get that Ordering object for DateTime. Is there?

In particular it'd be great to lose the asInstanceOf ...

Please refer to [How to define an Ordering in Scala?](http://stackoverflow.com/questions/9061141/how-to-define-an-ordering-in-scala) — pedram bashiri, Nov 11 '16 at 19:16

score 5 · Answer 1 · answered Mar 12 '12 at 14:31

Another possibility is to use comparatorToOrdering:

Ordering.comparatorToOrdering(DateTimeComparator.getInstance.asInstanceOf[Comparator[DateTime]])

I suppose that's what the asScala call does. It's not prettier, I know :-|

(The cast is unfortunately required because DateTimeComparator implements Comparator as a raw type.)

score 4 · Answer 2 · answered Dec 31 '13 at 11:51

You can also write your own class that extends the Ordering trait, and use this as input to the maximum function:

class JodaDateTimeOrdering extends Ordering[org.joda.time.DateTime] {
  val dtComparer = DateTimeComparator.getInstance()

  def compare(x: DateTime, y: DateTime): Int = {
    dtComparer.compare(x, y)
  }
}

score 1 · Answer 3 · answered Aug 17 '13 at 19:15

1

Best possibility, but with additional dependency: NScala-Time wrapper for Joda DateTime has DateTimeOrdering implicit:

https://github.com/nscala-time/nscala-time/blob/master/src/main/scala/com/github/nscala_time/time/Implicits.scala

answered Aug 17 '13 at 19:15

Alexander Chepurnoy

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huynhjl · Answer 4 · 2011-04-23T14:40:28.203

1

times.max(Ordering.fromLessThan[DateTime](
  DateTimeComparator.getInstance.compare(_,_) < 0))

which is ugly too!

Where does your asScala come from?

additional thoughts

I'm not sure there is a better way. DateComparator implements Comparator.

the max method expects an Ordering[DateTime]. Ordered and Ordering are invariant in Scala. So I think the case is necessary to use asScala.

edited Apr 23 '11 at 14:40

answered Apr 23 '11 at 03:23

huynhjl

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asScala is from scalaj.collection, it has a bunch of scala<->java converters – Havoc P Apr 23 '11 at 13:00

score 0 · Answer 5 · answered Aug 28 '14 at 22:16

0

In case you are willing to use Saddle, there's an implicit Datetime ordering defined there, in which case this is enough to solve the issue:

import org.saddle.time._

answered Aug 28 '14 at 22:16

Svend

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How to convert DateTimeComparator to an Ordering[DateTime] in Scala

5 Answers5