PERF: GH2003 Series.isin for categorical dtypes

asv_bench/benchmarks/categoricals.py

@@ -148,3 +148,18 @@ def time_rank_int_cat(self):
 
     def time_rank_int_cat_ordered(self):
         self.s_int_cat_ordered.rank()
+
+
+class Isin(object):
+
+    goal_time = 0.2
+
+    def setup(self):
+        n = 5 * 10**5
+        sample_size = 100
+        arr = ['s%04d' % i for i in np.random.randint(0, n // 10, size=n)]
+        self.sample = np.random.choice(arr, sample_size)
+        self.ts = pd.Series(arr).astype('category')
+
+    def time_isin_categorical_strings(self):
+        self.ts.isin(self.sample)

doc/source/whatsnew/v0.23.0.txt

@@ -896,6 +896,7 @@ Performance Improvements
 - Improved performance of :func:`pandas.core.groupby.GroupBy.ffill` and :func:`pandas.core.groupby.GroupBy.bfill` (:issue:`11296`)
 - Improved performance of :func:`pandas.core.groupby.GroupBy.any` and :func:`pandas.core.groupby.GroupBy.all` (:issue:`15435`)
 - Improved performance of :func:`pandas.core.groupby.GroupBy.pct_change` (:issue:`19165`)
+- Improved performance of :func:`Series.isin` in the case of categorical dtypes (:issue:`20003`)
 
 .. _whatsnew_0230.docs:
 

pandas/core/algorithms.py

@@ -407,6 +407,12 @@ def isin(comps, values):
     if not isinstance(values, (ABCIndex, ABCSeries, np.ndarray)):
         values = construct_1d_object_array_from_listlike(list(values))
 
+    if is_categorical_dtype(comps):
+        # handle categoricals
+        return comps._values.isin(values)
+
+    comps = com._values_from_object(comps)
+
     comps, dtype, _ = _ensure_data(comps)
     values, _, _ = _ensure_data(values, dtype=dtype)
 

pandas/core/arrays/categorical.py

@@ -39,6 +39,8 @@
 from pandas.util._decorators import (
     Appender, cache_readonly, deprecate_kwarg, Substitution)
 
+import pandas.core.algorithms as algorithms
+
 from pandas.io.formats.terminal import get_terminal_size
 from pandas.util._validators import validate_bool_kwarg, validate_fillna_kwargs
 from pandas.core.config import get_option
@@ -2216,6 +2218,60 @@ def _concat_same_type(self, to_concat):
     def _formatting_values(self):
         return self
 
+    def isin(self, values):
+        """
+        Check whether `values` are contained in Categorical.
+
+        Return a boolean NumPy Array showing whether each element in
+        the Categorical matches an element in the passed sequence of
+        `values` exactly.
+
+        Parameters
+        ----------
+        values : set or list-like
+            The sequence of values to test. Passing in a single string will
+            raise a ``TypeError``. Instead, turn a single string into a
+            list of one element.
+
+        Returns
+        -------
+        isin : numpy.ndarray (bool dtype)
+
+        Raises
+        ------
+        TypeError
+          * If `values` is a string
+
+        See Also
+        --------
+        pandas.Series.isin : equivalent method on Series
+
+        Examples
+        --------
+
+        >>> s = pd.Categorical(['lama', 'cow', 'lama', 'beetle', 'lama',
+        ...                'hippo'])
+        >>> s.isin(['cow', 'lama'])
+        array([ True,  True,  True, False,  True, False])
+
+        Passing a single string as ``s.isin('lama')`` will raise an error. Use
+        a list of one element instead:
+
+        >>> s.isin(['lama'])
+        array([ True, False,  True, False,  True, False])
+        """
+        if not is_list_like(values):
+            raise TypeError("only list-like objects are allowed to be passed"
+                            " to isin(), you passed a [{values_type}]"
+                            .format(values_type=type(values).__name__))
+        from pandas.core.series import _sanitize_array
+        values = _sanitize_array(values, None, None)
+        null_mask = np.asarray(isna(values))
+        code_values = self.categories.get_indexer(values)
+        code_values = code_values[null_mask | (code_values >= 0)]
+        return algorithms.isin(self.codes, code_values)
+
+
 # The Series.cat accessor
 
 

pandas/core/indexes/base.py

@@ -3487,7 +3487,7 @@ def isin(self, values, level=None):
         """
         if level is not None:
             self._validate_index_level(level)
-        return algos.isin(np.array(self), values)
+        return algos.isin(self, values)
 
     def _can_reindex(self, indexer):
         """

pandas/core/series.py

@@ -3564,7 +3564,7 @@ def isin(self, values):
         5    False
         Name: animal, dtype: bool
         """
-        result = algorithms.isin(com._values_from_object(self), values)
+        result = algorithms.isin(self, values)
         return self._constructor(result, index=self.index).__finalize__(self)
 
     def between(self, left, right, inclusive=True):

pandas/tests/categorical/test_algos.py

@@ -47,3 +47,25 @@ def test_factorized_sort_ordered():
 
     tm.assert_numpy_array_equal(labels, expected_labels)
     tm.assert_categorical_equal(uniques, expected_uniques)
+
+
+def test_isin_cats():
+    # GH2003
+    cat = pd.Categorical(["a", "b", np.nan])
+
+    result = cat.isin(["a", np.nan])
+    expected = np.array([True, False, True], dtype=bool)
+    tm.assert_numpy_array_equal(expected, result)
+
+    result = cat.isin(["a", "c"])
+    expected = np.array([True, False, False], dtype=bool)
+    tm.assert_numpy_array_equal(expected, result)
+
+
+@pytest.mark.parametrize("empty", [[], pd.Series(), np.array([])])
+def test_isin_empty(empty):
+    s = pd.Categorical(["a", "b"])
+    expected = np.array([False, False], dtype=bool)
+
+    result = s.isin(empty)
+    tm.assert_numpy_array_equal(expected, result)