Resolving #61086 : BUG: Collision between equivalent frequencies 'QS-…

…FEB' and 'QS-NOV'
pandas-dev · ycdjun · Mar 18, 2025 · Mar 19, 2025 · Mar 19, 2025 · Mar 20, 2025
commit 4bd0594096b699f6a2d36cf8340db5946783abdc
diff --git a/doc/source/whatsnew/v3.0.0.rst b/doc/source/whatsnew/v3.0.0.rst
@@ -75,6 +75,7 @@ Other enhancements
 - :meth:`pandas.concat` will raise a ``ValueError`` when ``ignore_index=True`` and ``keys`` is not ``None`` (:issue:`59274`)
 - :py:class:`frozenset` elements in pandas objects are now natively printed (:issue:`60690`)
 - Add ``"delete_rows"`` option to ``if_exists`` argument in :meth:`DataFrame.to_sql` deleting all records of the table before inserting data (:issue:`37210`).
+- Added :func:`DateTimeIndex.set_freq` and :class:`DateTimeIndex` now supports assigning equivalent quarerly start frequency (:issue:`61086`)
 - Added half-year offset classes :class:`HalfYearBegin`, :class:`HalfYearEnd`, :class:`BHalfYearBegin` and :class:`BHalfYearEnd` (:issue:`60928`)
 - Errors occurring during SQL I/O will now throw a generic :class:`.DatabaseError` instead of the raw Exception type from the underlying driver manager library (:issue:`60748`)
 - Implemented :meth:`Series.str.isascii` and :meth:`Series.str.isascii` (:issue:`59091`)

diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
@@ -2519,8 +2519,13 @@ def _validate_inferred_freq(
    -------
    freq : DateOffset or None
    """
+    offset1 = to_offset(freq)
+    offset2 = to_offset(inferred_freq)
+
+    freq_equal = type(offset1) == type(offset2)
+
    if inferred_freq is not None:
-        if freq is not None and freq != inferred_freq:
+        if freq is not None and not freq_equal:
            raise ValueError(
                f"Inferred frequency {inferred_freq} from passed "
                "values does not conform to passed frequency "

diff --git a/pandas/core/indexes/datetimes.py b/pandas/core/indexes/datetimes.py
@@ -421,6 +421,34 @@ def _can_range_setop(self, other) -> bool:

    # --------------------------------------------------------------------

+    def _set_freq(self, freq, *, inplace: bool = False):
+        """
+        Set a new frequency for this DatetimeIndex.
+
+        Parameters
+        ----------
+        freq : str, Timedelta, datetime.timedelta, or DateOffset, default 'S'
+            Frequency strings can have multiples, e.g. '5h'. See
+            :ref:`here <timeseries.offset_aliases>` for a list of
+            frequency aliases.
+        inplace : bool, default False
+            If True, modifies object in place. Otherwise, returns a new DateTimeIndex
+
+        Returns
+        -------
+        DatetimeIndex
+            Fixed frequency DatetimeIndex
+        """
+
+        if inplace:
+            self._freq = to_offset(freq)
+        else:
+            new_index = self.copy()
+            new_index.freq = to_offset(freq)
+            return new_index
+
+    # --------------------------------------------------------------------
+
    def _get_time_micros(self) -> npt.NDArray[np.int64]:
        """
        Return the number of microseconds since midnight.

diff --git a/pandas/tests/indexes/datetimes/test_constructors.py b/pandas/tests/indexes/datetimes/test_constructors.py
@@ -1204,3 +1204,12 @@ def test_dti_constructor_object_dtype_dayfirst_yearfirst_with_tz(self):
        result2 = DatetimeIndex([val], tz="US/Pacific", yearfirst=True)
        expected2 = DatetimeIndex([yfirst]).as_unit("s")
        tm.assert_index_equal(result2, expected2)
+
+    def test_datetimeindex_equivalent_freq(self):
+        idx2 = date_range("2020-02-01", freq="QS-FEB", periods=4)
+        new_idx2 = idx2._set_freq("QS-MAY")
+        tm.assert_index_equal(new_idx2, idx2)
+        assert new_idx2.freq == "QS-MAY"
+
+        idx2._set_freq("QS-MAY", inplace=True)
+        assert idx2.freq == "QS-MAY"
-Original file line number
+Diff line change
@@ -2519,8 +2519,13 @@ def _validate_inferred_freq(
         -------
         freq : DateOffset or None
         """
+        offset1 = to_offset(freq)
+        offset2 = to_offset(inferred_freq)
+        freq_equal = type(offset1) == type(offset2)
             Copy link

  
      
    
  

  
      

  
  Member


      

  

  
    
      

      
            rhshadrach
  

      

      

      


        Mar 19, 2025


      
    

  


        
      
  
  
  
    

    There was a problem hiding this comment.


  

 
  
    

    Choose a reason for hiding this comment

    
      The reason will be displayed to describe this comment to others. Learn more.
    

    
      
      


  


  
    
      I do not think this is sufficient, for example QuarterBegin: startingMonth=2 and QuarterBegin: startingMonth=3 will both have the same type, but are not the same frequency.
    
  
  


    

        
      
  
  
    
  
  
  
    
    Sorry, something went wrong.
  

  
    
  
    
      

              Uh oh!

              
There was an error while loading. Please reload this page.


  
  


          
      
  
    
    
      
        
            
    All reactions
         if inferred_freq is not None:
-            if freq is not None and freq != inferred_freq:
+            if freq is not None and not freq_equal:
                 raise ValueError(
                     f"Inferred frequency {inferred_freq} from passed "
                     "values does not conform to passed frequency "
-          Expand Down