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PERF: Faster comparisons of indexes when compared to self #37109

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PERF: Faster comparisons of indexes when compared to self #37109

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18 changes: 18 additions & 0 deletions pandas/core/indexes/base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5363,6 +5363,24 @@ def _cmp_method(self, other, op):
"""
Wrapper used to dispatch comparison operations.
"""
from .multi import MultiIndex

if self.is_(other) and not isinstance(self, MultiIndex):
# short-circuit when other is same as self
# if we're comparing equality, return an np.ones array, else an np.zeros arr
bool_arr_type, na_bool = {
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the pattern we use elsewhere is more like

res = np.empty(self.shape, dtype=bool)
res[:] = (op.__name__ in ["eq", "le", "ge"]
if self._can_hold_na:
   ...

operator.eq: (np.ones, False),
operator.le: (np.ones, False),
operator.ge: (np.ones, False),
operator.ne: (np.zeros, True),
operator.lt: (np.zeros, True),
operator.gt: (np.zeros, True),
}[op]
bool_arr = bool_arr_type(self.shape, dtype=bool)
if self._can_hold_na:
bool_arr[isna(self)] = na_bool
return bool_arr

if isinstance(other, (np.ndarray, Index, ABCSeries, ExtensionArray)):
if len(self) != len(other):
raise ValueError("Lengths must match to compare")
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