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REF: implement MultiIndex._get_indexer_level_0 #42480

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Jul 12, 2021
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REF: implement MultiIndex._get_indexer_level_0 #42480

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28 changes: 16 additions & 12 deletions pandas/core/indexes/multi.py
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Original file line number Diff line number Diff line change
Expand Up @@ -73,7 +73,6 @@
from pandas.core.arrays import Categorical
from pandas.core.arrays.categorical import factorize_from_iterables
import pandas.core.common as com
from pandas.core.indexers import is_empty_indexer
import pandas.core.indexes.base as ibase
from pandas.core.indexes.base import (
Index,
Expand Down Expand Up @@ -2559,24 +2558,29 @@ def _convert_listlike_indexer(self, keyarr) -> np.ndarray | None:

# are we indexing a specific level
if len(keyarr) and not isinstance(keyarr[0], tuple):
_, indexer = self.reindex(keyarr, level=0)

# take all
if indexer is None:
indexer = np.arange(len(self), dtype=np.intp)
return indexer

check = self.levels[0].get_indexer(keyarr)
mask = check == -1
indexer = self._get_indexer_level_0(keyarr)
mask = indexer == -1
if mask.any():
raise KeyError(f"{keyarr[mask]} not in index")
elif is_empty_indexer(indexer, keyarr):
check = self.levels[0].get_indexer(keyarr)
cmask = check == -1
if cmask.any():
raise KeyError(f"{keyarr[cmask]} not in index")
# We get here when levels still contain values which are not
# actually in Index anymore
raise KeyError(f"{keyarr} not in index")

return indexer

def _get_indexer_level_0(self, target) -> np.ndarray:
"""
Optimized equivalent to `self.get_level_values(0).get_indexer_for(target)`.
"""
lev = self.levels[0]
codes = self._codes[0]
cat = Categorical.from_codes(codes=codes, categories=lev)
ci = Index(cat)
return ci.get_indexer_for(target)

def _get_partial_string_timestamp_match_key(self, key):
"""
Translate any partial string timestamp matches in key, returning the
Expand Down