Strictly monotonic (#16555)

(cherry picked from commit cab2b6b)

Author: TomAugspurger

doc/source/api.rst

@@ -1286,6 +1286,8 @@ Attributes
    Index.is_monotonic
    Index.is_monotonic_increasing
    Index.is_monotonic_decreasing
+   Index.is_strictly_monotonic_increasing
+   Index.is_strictly_monotonic_decreasing
    Index.is_unique
    Index.has_duplicates
    Index.dtype

doc/source/whatsnew/v0.20.2.txt

@@ -21,6 +21,7 @@ Enhancements
 
 - Unblocked access to additional compression types supported in pytables: 'blosc:blosclz, 'blosc:lz4', 'blosc:lz4hc', 'blosc:snappy', 'blosc:zlib', 'blosc:zstd' (:issue:`14478`)
 - ``Series`` provides a ``to_latex`` method (:issue:`16180`)
+- Added :attr:`Index.is_strictly_monotonic_increasing` and :attr:`Index.is_strictly_monotonic_decreasing` properties (:issue:`16515`)
 
 .. _whatsnew_0202.performance:
 
@@ -56,7 +57,7 @@ Indexing
 ^^^^^^^^
 
 - Bug in ``DataFrame.reset_index(level=)`` with single level index (:issue:`16263`)
-
+- Bug in partial string indexing with a monotonic, but not strictly-monotonic, index incorrectly reversing the slice bounds (:issue:`16515`)
 
 I/O
 ^^^

pandas/core/indexes/base.py

@@ -1191,6 +1191,15 @@ def is_monotonic_increasing(self):
         """
         return if the index is monotonic increasing (only equal or
         increasing) values.
+
+        Examples
+        --------
+        >>> Index([1, 2, 3]).is_monotonic_increasing
+        True
+        >>> Index([1, 2, 2]).is_monotonic_increasing
+        True
+        >>> Index([1, 3, 2]).is_monotonic_increasing
+        False
         """
         return self._engine.is_monotonic_increasing
 
@@ -1199,9 +1208,50 @@ def is_monotonic_decreasing(self):
         """
         return if the index is monotonic decreasing (only equal or
         decreasing) values.
+
+        Examples
+        --------
+        >>> Index([3, 2, 1]).is_monotonic_decreasing
+        True
+        >>> Index([3, 2, 2]).is_monotonic_decreasing
+        True
+        >>> Index([3, 1, 2]).is_monotonic_decreasing
+        False
         """
         return self._engine.is_monotonic_decreasing
 
+    @property
+    def is_strictly_monotonic_increasing(self):
+        """return if the index is strictly monotonic increasing
+        (only increasing) values
+
+        Examples
+        --------
+        >>> Index([1, 2, 3]).is_strictly_monotonic_increasing
+        True
+        >>> Index([1, 2, 2]).is_strictly_monotonic_increasing
+        False
+        >>> Index([1, 3, 2]).is_strictly_monotonic_increasing
+        False
+        """
+        return self.is_unique and self.is_monotonic_increasing
+
+    @property
+    def is_strictly_monotonic_decreasing(self):
+        """return if the index is strictly monotonic decreasing
+        (only decreasing) values
+
+        Examples
+        --------
+        >>> Index([3, 2, 1]).is_strictly_monotonic_decreasing
+        True
+        >>> Index([3, 2, 2]).is_strictly_monotonic_decreasing
+        False
+        >>> Index([3, 1, 2]).is_strictly_monotonic_decreasing
+        False
+        """
+        return self.is_unique and self.is_monotonic_decreasing
+
     def is_lexsorted_for_tuple(self, tup):
         return True
 

pandas/core/indexes/datetimes.py

@@ -1472,7 +1472,7 @@ def _maybe_cast_slice_bound(self, label, side, kind):
             # the bounds need swapped if index is reverse sorted and has a
             # length > 1 (is_monotonic_decreasing gives True for empty
             # and length 1 index)
-            if self.is_monotonic_decreasing and len(self) > 1:
+            if self.is_strictly_monotonic_decreasing and len(self) > 1:
                 return upper if side == 'left' else lower
             return lower if side == 'left' else upper
         else:

pandas/tests/indexes/datetimes/test_datetime.py

@@ -774,3 +774,10 @@ def test_slice_bounds_empty(self):
         left = empty_idx._maybe_cast_slice_bound('2015-01-02', 'left', 'loc')
         exp = Timestamp('2015-01-02 00:00:00')
         assert left == exp
+
+    def test_slice_duplicate_monotonic(self):
+        # https://github.com/pandas-dev/pandas/issues/16515
+        idx = pd.DatetimeIndex(['2017', '2017'])
+        result = idx._maybe_cast_slice_bound('2017-01-01', 'left', 'loc')
+        expected = Timestamp('2017-01-01')
+        assert result == expected

pandas/tests/indexes/test_base.py

@@ -1330,8 +1330,10 @@ def test_tuple_union_bug(self):
 
     def test_is_monotonic_incomparable(self):
         index = Index([5, datetime.now(), 7])
-        assert not index.is_monotonic
+        assert not index.is_monotonic_increasing
         assert not index.is_monotonic_decreasing
+        assert not index.is_strictly_monotonic_increasing
+        assert not index.is_strictly_monotonic_decreasing
 
     def test_get_set_value(self):
         values = np.random.randn(100)
@@ -2030,6 +2032,8 @@ def test_is_monotonic_na(self):
         for index in examples:
             assert not index.is_monotonic_increasing
             assert not index.is_monotonic_decreasing
+            assert not index.is_strictly_monotonic_increasing
+            assert not index.is_strictly_monotonic_decreasing
 
     def test_repr_summary(self):
         with cf.option_context('display.max_seq_items', 10):

pandas/tests/indexes/test_multi.py

@@ -2373,22 +2373,30 @@ def test_is_monotonic(self):
         i = MultiIndex.from_product([np.arange(10),
                                      np.arange(10)], names=['one', 'two'])
         assert i.is_monotonic
+        assert i.is_strictly_monotonic_increasing
         assert Index(i.values).is_monotonic
+        assert i.is_strictly_monotonic_increasing
 
         i = MultiIndex.from_product([np.arange(10, 0, -1),
                                      np.arange(10)], names=['one', 'two'])
         assert not i.is_monotonic
+        assert not i.is_strictly_monotonic_increasing
         assert not Index(i.values).is_monotonic
+        assert not Index(i.values).is_strictly_monotonic_increasing
 
         i = MultiIndex.from_product([np.arange(10),
                                      np.arange(10, 0, -1)],
                                     names=['one', 'two'])
         assert not i.is_monotonic
+        assert not i.is_strictly_monotonic_increasing
         assert not Index(i.values).is_monotonic
+        assert not Index(i.values).is_strictly_monotonic_increasing
 
         i = MultiIndex.from_product([[1.0, np.nan, 2.0], ['a', 'b', 'c']])
         assert not i.is_monotonic
+        assert not i.is_strictly_monotonic_increasing
         assert not Index(i.values).is_monotonic
+        assert not Index(i.values).is_strictly_monotonic_increasing
 
         # string ordering
         i = MultiIndex(levels=[['foo', 'bar', 'baz', 'qux'],
@@ -2398,6 +2406,8 @@ def test_is_monotonic(self):
                        names=['first', 'second'])
         assert not i.is_monotonic
         assert not Index(i.values).is_monotonic
+        assert not i.is_strictly_monotonic_increasing
+        assert not Index(i.values).is_strictly_monotonic_increasing
 
         i = MultiIndex(levels=[['bar', 'baz', 'foo', 'qux'],
                                ['mom', 'next', 'zenith']],
@@ -2406,6 +2416,8 @@ def test_is_monotonic(self):
                        names=['first', 'second'])
         assert i.is_monotonic
         assert Index(i.values).is_monotonic
+        assert i.is_strictly_monotonic_increasing
+        assert Index(i.values).is_strictly_monotonic_increasing
 
         # mixed levels, hits the TypeError
         i = MultiIndex(
@@ -2416,6 +2428,20 @@ def test_is_monotonic(self):
             names=['household_id', 'asset_id'])
 
         assert not i.is_monotonic
+        assert not i.is_strictly_monotonic_increasing
+
+    def test_is_strictly_monotonic(self):
+        idx = pd.MultiIndex(levels=[['bar', 'baz'], ['mom', 'next']],
+                            labels=[[0, 0, 1, 1], [0, 0, 0, 1]])
+        assert idx.is_monotonic_increasing
+        assert not idx.is_strictly_monotonic_increasing
+
+    @pytest.mark.xfail(reason="buggy MultiIndex.is_monotonic_decresaing.")
+    def test_is_strictly_monotonic_decreasing(self):
+        idx = pd.MultiIndex(levels=[['baz', 'bar'], ['next', 'mom']],
+                            labels=[[0, 0, 1, 1], [0, 0, 0, 1]])
+        assert idx.is_monotonic_decreasing
+        assert not idx.is_strictly_monotonic_decreasing
 
     def test_reconstruct_sort(self):
 

pandas/tests/indexes/test_numeric.py

@@ -465,16 +465,36 @@ def test_view(self):
     def test_is_monotonic(self):
         assert self.index.is_monotonic
         assert self.index.is_monotonic_increasing
+        assert self.index.is_strictly_monotonic_increasing
         assert not self.index.is_monotonic_decreasing
+        assert not self.index.is_strictly_monotonic_decreasing
 
         index = self._holder([4, 3, 2, 1])
         assert not index.is_monotonic
-        assert index.is_monotonic_decreasing
+        assert not index.is_strictly_monotonic_increasing
+        assert index.is_strictly_monotonic_decreasing
 
         index = self._holder([1])
         assert index.is_monotonic
         assert index.is_monotonic_increasing
         assert index.is_monotonic_decreasing
+        assert index.is_strictly_monotonic_increasing
+        assert index.is_strictly_monotonic_decreasing
+
+    def test_is_strictly_monotonic(self):
+        index = self._holder([1, 1, 2, 3])
+        assert index.is_monotonic_increasing
+        assert not index.is_strictly_monotonic_increasing
+
+        index = self._holder([3, 2, 1, 1])
+        assert index.is_monotonic_decreasing
+        assert not index.is_strictly_monotonic_decreasing
+
+        index = self._holder([1, 1])
+        assert index.is_monotonic_increasing
+        assert index.is_monotonic_decreasing
+        assert not index.is_strictly_monotonic_increasing
+        assert not index.is_strictly_monotonic_decreasing
 
     def test_logical_compat(self):
         idx = self.create_index()

pandas/tests/indexes/test_range.py

@@ -331,25 +331,35 @@ def test_is_monotonic(self):
         assert self.index.is_monotonic
         assert self.index.is_monotonic_increasing
         assert not self.index.is_monotonic_decreasing
+        assert self.index.is_strictly_monotonic_increasing
+        assert not self.index.is_strictly_monotonic_decreasing
 
         index = RangeIndex(4, 0, -1)
         assert not index.is_monotonic
+        assert not index.is_strictly_monotonic_increasing
         assert index.is_monotonic_decreasing
+        assert index.is_strictly_monotonic_decreasing
 
         index = RangeIndex(1, 2)
         assert index.is_monotonic
         assert index.is_monotonic_increasing
         assert index.is_monotonic_decreasing
+        assert index.is_strictly_monotonic_increasing
+        assert index.is_strictly_monotonic_decreasing
 
         index = RangeIndex(2, 1)
         assert index.is_monotonic
         assert index.is_monotonic_increasing
         assert index.is_monotonic_decreasing
+        assert index.is_strictly_monotonic_increasing
+        assert index.is_strictly_monotonic_decreasing
 
         index = RangeIndex(1, 1)
         assert index.is_monotonic
         assert index.is_monotonic_increasing
         assert index.is_monotonic_decreasing
+        assert index.is_strictly_monotonic_increasing
+        assert index.is_strictly_monotonic_decreasing
 
     def test_equals_range(self):
         equiv_pairs = [(RangeIndex(0, 9, 2), RangeIndex(0, 10, 2)),