def rowgroupmap(table, key, mapper, header=None, presorted=False,
                buffersize=None, tempdir=None, cache=True):

    return RowGroupMapView(table, key, mapper, header=header,
                           presorted=presorted,
                           buffersize=buffersize, tempdir=tempdir, cache=cache)
Group rows under the given key then apply `mapper` to yield zero or more
dataset/ETHPy150Open alimanfoo/petl/petl/transform/maps.py/rowgroupmap