On Friday, 21 March 2014 at 16:53:46 UTC, H. S. Teoh wrote:
Be aware, though, that groupBy only compares *adjacent* elements for equivalence; it does not sort the input. So if your input has equivalent elements interspersed with non-equivalent elements, you will have theequivalent elements split into multiple runs in the output.
I think that's why Justin used sort. The hashGroupBy proposed by bearophile would avoid the sort and the additional memory usage though, so that would be even better.
