Rebased; copy if datetime

Author: GuessWhoSamFoo

pandas/core/algorithms.py

@@ -219,6 +219,10 @@ 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':