Translate slice objects to concatenation along the first axis.
This is the masked array version of lib.index_tricks.RClass.
See also
lib.index_tricks.RClass
Examples
>>> np.ma.mr_[np.ma.array([1,2,3]), 0, 0, np.ma.array([4,5,6])]
array([1, 2, 3, 0, 0, 4, 5, 6])