wmde/WikibaseDataModel — pull request #199 by Benestar (2014-09-18 21:19:46+00:00)
Title: [WIP] Create initial version of ByPropertyIdGrouper

This is some initial idea to fix #190. It aims to be a lightweight alternative to `ByPropertyIdArray` by not providing any editing methods but only indexing and querying the data.

### TODO
* Finish tests
* Use in #198