DOC: Added reverse rolling window examples

doc/source/user_guide/window.rst

@@ -198,6 +198,36 @@ from present information back to past information. This allows the rolling windo
 
    df
 
+.. _window.reverse_rolling_window:
+
+Reverse rolling window
+~~~~~~~~~~~~~~~~~~~~~~
+
+Get the window of a rolling function to look forward.
+
+Examples:
+
+.. ipython:: python
+
+   # Using slicing
+   # apply the rolling aggregation and then flip the result.
+   df = pd.DataFrame(data=[[pd.Timestamp('2018-01-01 00:00:00'), 100],
+                           [pd.Timestamp('2018-01-01 00:00:01'), 101],
+                           [pd.Timestamp('2018-01-01 00:00:03'), 103],
+                           [pd.Timestamp('2018-01-01 00:00:04'), 111]],
+                     columns=['time', 'value']).set_index('time')
+   df
+
+   df1 = df[::-1].rolling('2s').sum()[::-1]
+   df1
+
+   # Using FixedForwardWindowIndexer
+   # Creates window boundaries for fixed-length windows that include the current row.
+   indexer = pd.api.indexers.FixedForwardWindowIndexer(window_size=2)
+
+   df2 = df.rolling(window=indexer, min_periods=1).sum()
+   df2
+
 
 .. _window.custom_rolling_window: