add IntervalIndex.get_loc_exact

doc/source/whatsnew/v0.23.0.txt

@@ -507,6 +507,7 @@ Other API Changes
 - Set operations (union, difference...) on :class:`IntervalIndex` with incompatible index types will now raise a ``TypeError`` rather than a ``ValueError`` (:issue:`19329`)
 - :class:`DateOffset` objects render more simply, e.g. "<DateOffset: days=1>" instead of "<DateOffset: kwds={'days': 1}>" (:issue:`19403`)
 - :func:`pandas.merge` provides a more informative error message when trying to merge on timezone-aware and timezone-naive columns (:issue:`15800`)
+- New :meth:`IntervalIndex.get_loc_exact` has been added to find exact Interval matches only (:issue:`19349`)
 
 .. _whatsnew_0230.deprecations:
 

pandas/core/indexes/interval.py

@@ -903,11 +903,8 @@ def _get_loc_only_exact_matches(self, key):
             if not self.is_unique:
                 raise ValueError("cannot index with a slice Interval"
                                  " and a non-unique index")
-
-            # TODO: this expands to a tuple index, see if we can
-            # do better
-            return Index(self._multiindex.values).get_loc(key)
-        raise KeyError
+            return super(IntervalIndex, self)._engine.get_loc(key)
+        raise KeyError(key)
 
     def _find_non_overlapping_monotonic_bounds(self, key):
         if isinstance(key, IntervalMixin):
@@ -970,6 +967,10 @@ def get_loc(self, key, method=None):
         >>> overlapping_index = pd.IntervalIndex([i2, i3])
         >>> overlapping_index.get_loc(1.5)
         array([0, 1], dtype=int64)
+
+        See Also
+        --------
+        get_loc_exact : Exact matches only
         """
         self._check_method(method)
 
@@ -1003,6 +1004,47 @@ def get_loc(self, key, method=None):
             else:
                 return self._engine.get_loc(key)
 
+    def get_loc_exact(self, key, method=None):
+        """Get integer location, slice or boolean mask for exact
+        Interval matches only.
+
+        Parameters
+        ----------
+        key : Interval
+            The label we want to find locations for. Must have type
+            :class:`Interval`
+        method : {None}, optional
+            * default: matches where the label exactly matches a given
+              :class:`Interval`.
+
+        Returns
+        -------
+        loc : int if unique index, slice if monotonic index, else mask
+
+        Examples
+        ---------
+        >>> i1, i2 = pd.Interval(0, 1), pd.Interval(1, 2)
+        >>> index = pd.IntervalIndex([i1, i2])
+        >>> index.get_loc_exact(i1)
+        0
+
+        If an exact match is not found, a KeyError is raised
+        >>> index.get_loc_exact(pd.Interval(0.5, 1.5))
+        KeyError: Interval(0.5, 1.5, closed='right')
+
+        If a label is in several locations, you get all the relevant
+        locations.
+
+        >>> index = pd.IntervalIndex([i1, i2, i1])
+        >>> index.get_loc_exact(i1)
+        array([ True, False,  True], dtype=bool)
+
+        See Also
+        --------
+        get_loc
+        """
+        return self.astype(object).get_loc(key, method=method)
+
     def get_value(self, series, key):
         if com.is_bool_indexer(key):
             loc = key

pandas/tests/indexes/interval/test_interval.py

@@ -497,6 +497,23 @@ def test_get_loc_interval(self):
         pytest.raises(KeyError, self.index.get_loc,
                       Interval(-1, 0, 'left'))
 
+    # To be removed, replaced by test_interval_new.py (see #16316, #16386)
+    def test_get_loc_exact(self):
+        # GH19353
+        assert self.index.get_loc_exact(Interval(0, 1)) == 0
+        with pytest.raises(KeyError):
+            self.index.get_loc_exact(1)
+        with pytest.raises(KeyError):
+            self.index.get_loc_exact(Interval(0, 1, 'left'))
+        with pytest.raises(KeyError):
+            self.index.get_loc_exact(Interval(0, 0.5))
+        with pytest.raises(KeyError):
+            self.index.get_loc_exact(Interval(2, 3))
+        with pytest.raises(KeyError):
+            self.index.get_loc_exact(Interval(-1, 0, 'left'))
+        # See #19353#issuecomment-364295029
+        self.index.get_loc(Interval(0, 1))
+
     # To be removed, replaced by test_interval_new.py (see #16316, #16386)
     def test_get_indexer(self):
         actual = self.index.get_indexer([-1, 0, 0.5, 1, 1.5, 2, 3])

pandas/tests/indexing/interval/test_interval.py

@@ -136,7 +136,7 @@ def test_with_slices(self):
             s[Interval(3, 6):]
 
         expected = s.iloc[3:5]
-        result = s[[Interval(3, 6)]]
+        result = s[Interval(3, 6)]
         tm.assert_series_equal(expected, result)
 
         # slice of scalar with step != 1