move error handling; doc fixups

Author: chris-b1

doc/source/timeseries.rst

@@ -1473,6 +1473,28 @@ Furthermore, you can also specify multiple aggregation functions for each column
    r.agg({'A' : ['sum','std'], 'B' : ['mean','std'] })
 
 
+If a ``DataFrame`` does not have a ``DatetimeIndex``, but instead you want
+to resample based on column in the frame, it can passed to the ``on`` keyword.
+
+.. ipython:: python
+
+   df = pd.DataFrame({'date': pd.date_range('2015-01-01', freq='W', periods=5),
+                      'a': np.arange(5)},
+                     index=pd.MultiIndex.from_arrays([
+                              [1,2,3,4,5],
+                              pd.date_range('2015-01-01', freq='W', periods=5)],
+                          names=['v','d']))
+   df
+   df.resample('M', on='date').sum()
+
+Similarly, if you instead want to resample by a level of ``MultiIndex``, its
+name or location can be passed to the ``level`` keyword.
+
+.. ipython:: python
+
+   df.resample(level='d').sum()
+
+
 .. _timeseries.periods:
 
 Time Span Representation

doc/source/whatsnew/v0.19.0.txt

@@ -377,7 +377,7 @@ Other enhancements
 
     pd.Timestamp(year=2012, month=1, day=1, hour=8, minute=30)
 
-- the ``.resample()`` function now accepts a ``on=`` or ``key=`` parameter for resampling on a column or ``MultiIndex`` level (:issue:`13500`)
+- the ``.resample()`` function now accepts a ``on=`` or ``level=`` parameter for resampling on a column or ``MultiIndex`` level (:issue:`13500`)
 
   .. ipython:: python
 

pandas/core/generic.py

@@ -4169,11 +4169,6 @@ def resample(self, rule, how=None, axis=0, fill_method=None, closed=None,
         """
         from pandas.tseries.resample import (resample,
                                              _maybe_process_deprecations)
-        if is_list_like(on):
-            raise ValueError("Only a single column may be passed to on")
-        if is_list_like(level):
-            raise ValueError("Only a single column may be passed to level")
-
         axis = self._get_axis_number(axis)
         r = resample(self, freq=rule, label=label, closed=closed,
                      axis=axis, kind=kind, loffset=loffset,

pandas/tseries/tests/test_resample.py

@@ -608,17 +608,24 @@ def test_api_validation(self):
         actual = df.resample('M', on='date').sum()
         assert_frame_equal(actual, expected)
 
-        actual = df.resample('M', level='d').sum()
         expected.index.name = 'd'
+        actual = df.resample('M', level='d').sum()
+        assert_frame_equal(actual, expected)
+
+        actual = df.resample('M', level=1).sum()
         assert_frame_equal(actual, expected)
 
+        # non DatetimeIndex
+        with tm.assertRaises(TypeError):
+            df.resample('M', level='v')
+
         with tm.assertRaises(ValueError):
             df.resample('M', on='date', level='d')
 
-        with tm.assertRaises(ValueError):
+        with tm.assertRaises(TypeError):
             df.resample('M', on=['a', 'date'])
 
-        with tm.assertRaises(ValueError):
+        with tm.assertRaises(KeyError):
             df.resample('M', level=['a', 'date'])