[Matrix]: unit test of groupby on EM matrix.
[Matrix]: unit test of groupby on EM matrix.

flashxio/FlashX,icoming/FlashX,icoming/FlashX,icoming/FlashX,icoming/FlashX,flashxio/FlashX,flashxio/FlashX,flashxio/FlashX,flashxio/FlashX,icoming/FlashX,flashxio/FlashX