modify whatsnew

Author: peterpanmj

doc/source/whatsnew/v0.22.0.txt

@@ -37,6 +37,87 @@ The :func:`get_dummies` now accepts a ``dtype`` argument, which specifies a dtyp
 Other Enhancements
 ^^^^^^^^^^^^^^^^^^
 
+``Series.rank`` ``DataFrame.rank`` now can handle ``inf`` values and missing values properly
+""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+
+In previous versions, ``inf`` elements were assigned ``NaN`` as their ranks. Now ranks are calculated properly. (:issue:`6945`)
+
+Previous Behavior
+
+.. code-block:: ipython
+
+    In [17]: pd.Series([-np.inf, 0, 1, np.inf]).rank()
+    Out[17]:
+    0    1.0
+    1    2.0
+    2    3.0
+    3    NaN
+
+Current Behavior
+
+.. ipython:: ipython
+
+    In [5]:  pd.Series([-np.inf, 0, 1, np.inf]).rank()
+    Out[5]:
+    0    1.0
+    1    2.0
+    2    3.0
+    3    4.0
+    dtype: float64
+
+Furthermore, in previous versions, missing values were not distinguished from infinit values in the calculation.
+
+Previous Behavior
+
+.. code-block:: ipython
+
+    In [15]: pd.Series([np.nan, np.nan, -np.inf, -np.inf]).rank(na_option='top')
+    Out[15]:
+    0    2.5
+    1    2.5
+    2    2.5
+    3    2.5
+    dtype: float64
+
+Current Behavior
+
+.. ipython:: ipython
+
+    In [4]:  pd.Series([np.nan, np.nan, -np.inf, -np.inf]).rank(na_option='top')
+    Out[4]:
+    0    1.5
+    1    1.5
+    2    3.5
+    3    3.5
+    dtype: float64
+
+Moreover, previously, if you rank an array of ``object`` dtype, ``None`` values would be assigned different ranks.
+
+Previous Behavior
+
+.. code-block:: ipython
+
+    In [3]:  pd.Series([None, None, None, 'A', 'B']).rank(na_option='top')
+    Out[3]:
+    0    3.0
+    1    2.0
+    2    1.0
+    3    4.0
+    4    5.0
+    dtype: float64
+
+Current Behavior
+
+.. ipython:: ipython
+
+    In [3]:  pd.Series([None, None, None, 'A', 'B']).rank(na_option='top')
+    Out[3]:
+    0    2.0
+    1    2.0
+    2    2.0
+    3    4.0
+    4    5.0
+
 - Better support for :func:`Dataframe.style.to_excel` output with the ``xlsxwriter`` engine. (:issue:`16149`)
 - :func:`pandas.tseries.frequencies.to_offset` now accepts leading '+' signs e.g. '+1h'. (:issue:`18171`)
 - :func:`MultiIndex.unique` now supports the ``level=`` argument, to get unique values from a specific index level (:issue:`17896`)
@@ -189,7 +270,7 @@ Reshaping
 Numeric
 ^^^^^^^
 
--
+- Bug in :func:`Series.rank` and `DataFrame.rank` could not properly rank infinit values. Infinit values were assigned ``NaN`` as ranks. If missing values were present together with infinit values, the ranks were not properly calculated (:issue:`6945`)
 -
 -