Fixed whatsnew; copy value in rank_1d

Author: GuessWhoSamFoo

doc/source/whatsnew/v0.22.0.txt

@@ -335,7 +335,5 @@ Categorical
 Other
 ^^^^^
 
-- Improved error message when attempting to use a Python keyword as an identifier in a numexpr query (:issue:`18221`)
-- Fixed a bug where creating a Series from an array that contains both tz-naive and tz-aware values will result in a Series whose dtype is tz-aware instead of object (:issue:`16406`)
-- Adding a ``Period`` object to a ``datetime`` or ``Timestamp`` object will now correctly raise a ``TypeError`` (:issue:`17983`)
+- Improved error message when attempting to use a Python keyword as an identifier in a ``numexpr`` backed query (:issue:`18221`)
 - Bug in :func:`Series.rank` where ``Series`` containing ``NaT`` modifies the ``Series`` inplace (:issue:`18521`)

pandas/_libs/algos_rank_helper.pxi.in

@@ -84,6 +84,9 @@ def rank_1d_{{dtype}}(object in_arr, ties_method='average', ascending=True,
     mask = np.isnan(values)
     {{elif dtype == 'int64'}}
     mask = values == iNaT
+    # create copy in case of iNaT
+    if mask.any():
+        values = values.copy()
     {{endif}}
 
     # double sort first by mask and then by values to ensure nan values are

pandas/core/algorithms.py

@@ -219,10 +219,6 @@ def _get_data_algo(values, func_map):
     if is_categorical_dtype(values):
         values = values._values_for_rank()
 
-    # Create copy in case NaT converts to asi8
-    if is_datetime64_any_dtype(values):
-        values = values.copy()
-
     values, dtype, ndtype = _ensure_data(values)
     if ndtype == 'object':