PERF: always use hash-map for isin rather than np.isin1d

Author: realead

pandas/core/algorithms.py

@@ -433,19 +433,9 @@ def isin(comps: AnyArrayLike, values: AnyArrayLike) -> np.ndarray:
     comps, dtype = _ensure_data(comps)
     values, _ = _ensure_data(values, dtype=dtype)
 
-    # faster for larger cases to use np.in1d
     f = htable.ismember_object
 
-    # GH16012
-    # Ensure np.in1d doesn't get object types or it *may* throw an exception
-    if len(comps) > 1_000_000 and not is_object_dtype(comps):
-        # If the the values include nan we need to check for nan explicitly
-        # since np.nan it not equal to np.nan
-        if isna(values).any():
-            f = lambda c, v: np.logical_or(np.in1d(c, v), np.isnan(c))
-        else:
-            f = np.in1d
-    elif is_integer_dtype(comps):
+    if is_integer_dtype(comps):
         try:
             values = values.astype("int64", copy=False)
             comps = comps.astype("int64", copy=False)