def sum(self, values, axis=0, dtype=None):
    'compute the sum over each group\n\n        Parameters\n        ----------\n        values : array_like, [keys, ...]\n            values to sum per group\n        axis : int, optional\n            alternative reduction axis for values\n        dtype : output dtype\n\n        Returns\n        -------\n        unique: ndarray, [groups]\n            unique keys\n        reduced : ndarray, [groups, ...]\n            value array, reduced over groups\n        '
    values = np.asarray(values)
    return (self.unique, self.reduce(values, axis=axis, dtype=dtype))
compute the sum over each group

Parameters
----------
values : array_like, [keys, ...]
    values to sum per group
axis : int, optional
    alternative reduction axis for values
dtype : output dtype

Returns
-------
unique: ndarray, [groups]
    unique keys
reduced : ndarray, [groups, ...]
    value array, reduced over groups
def sum(self, values, axis=0, dtype=None):
    'compute the sum over each group\n\n        Parameters\n        ----------\n        values : array_like, [keys, ...]\n            values to sum per group\n        axis : int, optional\n            alternative reduction axis for values\n        dtype : output dtype\n\n        Returns\n        -------\n        unique: ndarray, [groups]\n            unique keys\n        reduced : ndarray, [groups, ...]\n            value array, reduced over groups\n        '
    values = np.asarray(values)
    return (self.unique, self.reduce(values, axis=axis, dtype=dtype))