Basically, DataType.compare() just calls the compareTo() method of the two objects after checking that the two types are the same. However, DataType.compare() does 2 things more than a simple compareTo().
Firts, it is specialized for Maps, for which sizes are taken into account and keys are sorted. Second, it imposes an (arbitrary) order on different data types. In this way the types are not dependent on each other and there is a single point of control. So I think you should use DataType.compare() unless you are sure you do not need these features. Anyway, there is something that I do not understand. What I do not understand is why the function needs to switch on the datatype byte and cast the objects before calling the compareTo on them. Just casting them to Comparable and letting Java run the proper polymorphic method should work as well, right? On Wed, Apr 28, 2010 at 07:12, hc busy <hc.b...@gmail.com> wrote: > guys, I'm implementing that ExtremalTupleByNthField and I have a question > about comparison... > > > So, when I have parsed out the two objects that I want to compare how do I > perform that comparison? My current implementation assumes the data is > Comparable (which they invariably are within pig) so I do > > > int c = ((Comparable)o1).compareTo((Comparable)o2); > > > now I also see that there's another compare that compares the two objects > by: > > > int c = DataType.compare(o1, o2, DataType.findType(o1), > DataType.findType(o2)); > > > > The initial methods works for all types I've tried (int, string, etc.) But > the latter is used by another UDF already in SVN. > > What are your suggestions? > > (PIG-1386 is ticket where I've checked in the patch). >
