def _make_indexer(self, self_indexer: Index, other_indexer: Index):
if self.aggregation_required:
group_ints, group_order = other_indexer.factorize()
self.other_grouper = group_ints
self.flat_indexer, self.missing_indices = group_order.get_indexer_non_unique(
self_indexer)
else: # Performance-tuned fast paths for constructing indexers
if self_indexer.equals(other_indexer): # Indexers are identical
self.flat_indexer = np.arange(len(other_indexer))
self.missing_indices = np.array([], dtype=int)
elif len(self_indexer.difference(
other_indexer)) == 0: # No missing values
# Taking the difference is faster than `all(.isin())`
self.missing_indices = np.array([], dtype=int)
self.flat_indexer = other_indexer.get_indexer(self_indexer)
else: # All other cases
self.flat_indexer, self.missing_indices = other_indexer.get_indexer_non_unique(
self_indexer)
