[Matrix]: use virtual matrices for groupby results.
[Matrix]: use virtual matrices for groupby results.

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