[datatable-help] First := by group demo

[Matthew Dowle]

All,

I don't usually forward S.O. Q&A here, but this one is a bit of a
milestone. First time := by group is being used but it's also using
grouping by i (rather than by by) with join inherited scope too.

http://stackoverflow.com/questions/11030614/how-to-best-join-one-column-of-a-data-table-with-another-column-of-the-same-data/11037016#11037016

Matthew