[Matrix]: one more test for groupby on data frame.
[Matrix]: one more test for groupby on data frame.

icoming/FlashGraph,flashxio/FlashX,icoming/FlashGraph,icoming/FlashX,flashxio/FlashX,flashxio/FlashX,icoming/FlashX,icoming/FlashX,flashxio/FlashX,zheng-da/FlashX,icoming/FlashX,zheng-da/FlashX,icoming/FlashGraph,flashxio/FlashX,icoming/FlashGraph,zheng-da/FlashX,zheng-da/FlashX,zheng-da/FlashX,icoming/FlashX,icoming/FlashGraph,flashxio/FlashX