Function xgboost_sys::XGDMatrixSetGroup

pub unsafe extern "C" fn XGDMatrixSetGroup(
    handle: DMatrixHandle,
    group: *const c_uint,
    len: bst_ulong
) -> c_int

\brief set label of the training matrix \param handle a instance of data matrix \param group pointer to group size \param len length of array \return 0 when success, -1 when failure happens