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implement arith ops on pd.Categorical #21213

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implement arith ops on pd.Categorical #21213

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34 changes: 34 additions & 0 deletions pandas/core/arrays/categorical.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
# pylint: disable=E1101,W0232
import operator

import numpy as np
from warnings import warn
Expand Down Expand Up @@ -60,6 +61,21 @@
Use 'allow_fill=False' to accept the new behavior.""")


def _cat_arithmetic_op(op, reverse=False):
# arithmetic operations are disabled
def func(self, other):
from pandas.core.ops import _get_opstr
str_rep = _get_opstr(op, self.__class__)
raise TypeError("{typ} cannot perform the operation "
"{op}".format(typ=type(self).__name__, op=str_rep))

opname = op.__name__
if reverse:
opname = '__r' + opname[2:]
func.__name__ = opname
return func


def _cat_compare_op(op):
def f(self, other):
# On python2, you can usually compare any type to any type, and
Expand Down Expand Up @@ -1203,6 +1219,24 @@ def map(self, mapper):
__le__ = _cat_compare_op('__le__')
__ge__ = _cat_compare_op('__ge__')

__add__ = _cat_arithmetic_op(operator.add)
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so my ops PR does almost exactly this (for extension arrays). I think we should maybe put it in a mixin? so can capture ops definitions generically (but of course can do that later).

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@jbrockmendel jbrockmendel May 25, 2018 •
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That's a good idea. For the most part I'm happy being hands-off with Categorical since others are more familiar with it. I figured this would be an easy way to demonstrate what I have in mind for discussions in #21160, #20889.

__radd__ = _cat_arithmetic_op(operator.add, True)
__sub__ = _cat_arithmetic_op(operator.sub)
__rsub__ = _cat_arithmetic_op(operator.sub, True)
__mul__ = _cat_arithmetic_op(operator.mul)
__rmul__ = _cat_arithmetic_op(operator.mul, True)
__truediv__ = _cat_arithmetic_op(operator.truediv)
__rtruediv__ = _cat_arithmetic_op(operator.truediv, True)
__floordiv__ = _cat_arithmetic_op(operator.floordiv)
__rfloordiv__ = _cat_arithmetic_op(operator.floordiv, True)
__mod__ = _cat_arithmetic_op(operator.mod)
__rmod__ = _cat_arithmetic_op(operator.mod, True)
__pow__ = _cat_arithmetic_op(operator.pow)
__rpow__ = _cat_arithmetic_op(operator.pow, True)
if compat.PY2:
__div__ = __truediv__
__rdiv__ = __rtruediv__

# for Series/ndarray like compat
@property
def shape(self):
Expand Down
7 changes: 5 additions & 2 deletions pandas/core/ops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1055,8 +1055,11 @@ def wrapper(left, right):
dtype=result.dtype)

elif is_categorical_dtype(left):
raise TypeError("{typ} cannot perform the operation "
"{op}".format(typ=type(left).__name__, op=str_rep))
# raises TypeError
result = dispatch_to_index_op(op, left, right, pd.Categorical)
return construct_result(left, result,
index=left.index, name=res_name,
dtype=result.dtype)

lvalues = left.values
rvalues = right
Expand Down