DOC: Clarify use of resample bins (#14888) (#17940)

Author: reidy-p

doc/source/timeseries.rst

@@ -1492,12 +1492,31 @@ labels.
 
 .. ipython:: python
 
-   ts.resample('5Min').mean() # by default label='right'
+   ts.resample('5Min').mean() # by default label='left'
 
    ts.resample('5Min', label='left').mean()
 
    ts.resample('5Min', label='left', loffset='1s').mean()
 
+.. note::
+
+    The default values for ``label`` and ``closed`` is 'left' for all 
+    frequency offsets except for 'M', 'A', 'Q', 'BM', 'BA', 'BQ', and 'W' 
+    which all have a default of 'right'.
+
+    .. ipython:: python
+
+       rng2 = pd.date_range('1/1/2012', end='3/31/2012', freq='D')
+       ts2 = pd.Series(range(len(rng2)), index=rng2)
+
+       # default: label='right', closed='right'
+       ts2.resample('M').max()
+
+       # default: label='left', closed='left'
+       ts2.resample('SM').max()
+
+       ts2.resample('SM', label='right', closed='right').max()
+
 The ``axis`` parameter can be set to 0 or 1 and allows you to resample the
 specified axis for a ``DataFrame``.
 

pandas/core/generic.py

@@ -5362,9 +5362,13 @@ def resample(self, rule, how=None, axis=0, fill_method=None, closed=None,
             the offset string or object representing target conversion
         axis : int, optional, default 0
         closed : {'right', 'left'}
-            Which side of bin interval is closed
+            Which side of bin interval is closed. The default is 'left'
+            for all frequency offsets except for 'M', 'A', 'Q', 'BM',
+            'BA', 'BQ', and 'W' which all have a default of 'right'.
         label : {'right', 'left'}
-            Which bin edge label to label bucket with
+            Which bin edge label to label bucket with. The default is 'left'
+            for all frequency offsets except for 'M', 'A', 'Q', 'BM',
+            'BA', 'BQ', and 'W' which all have a default of 'right'.
         convention : {'start', 'end', 's', 'e'}
             For PeriodIndex only, controls whether to use the start or end of
             `rule`
@@ -5424,7 +5428,7 @@ def resample(self, rule, how=None, axis=0, fill_method=None, closed=None,
         value in the bucket used as the label is not included in the bucket,
         which it labels. For example, in the original series the
         bucket ``2000-01-01 00:03:00`` contains the value 3, but the summed
-        value in the resampled bucket with the label``2000-01-01 00:03:00``
+        value in the resampled bucket with the label ``2000-01-01 00:03:00``
         does not include 3 (if it did, the summed value would be 6, not 3).
         To include this value close the right side of the bin interval as
         illustrated in the example below this one.