title: pandas drop rows on groupby level 2 sum or mean conditions
body: <p>I want to drop a group (all rows in the group) if the sum of values in a group is equal to a certain value.</p>
  
  <p>The following code provides an example:</p>
  
  <pre><code>&gt;&gt;&gt; df = pd.DataFrame(randn(10,10), index=pd.date_range('20130101',periods=10,freq='T'))
  &gt;&gt;&gt; df = pd.DataFrame(df.stack(), columns=['Values'])
  &gt;&gt;&gt; df.index.names = ['Time', 'Group']
  &gt;&gt;&gt; df.head(12)
  
                               Values
  Time                Group   
  2013-01-01 00:00:00   0    0.541795
                        1    0.060798
                        2    0.074224
                        3   -0.006818
                        4    1.211791
                        5   -0.066994
                        6   -1.019984
                        7   -0.558134
                        8    2.006748
                        9    2.737199
  2013-01-01 00:01:00   0    1.655502
                        1    0.376214
  
  &gt;&gt;&gt; df['Values'].groupby('Group').sum()
  
  Group
  0    3.754481
  1   -5.234744
  2   -2.000393
  3    0.991431
  4    3.930547
  5   -3.137915
  6   -1.260719
  7    0.145757
  8   -1.832132
  9    4.258525
  Name: Values, dtype: float64
  </code></pre>
  
  <p>So the question is; how can I for instance drop all group rows where the grouped sum is negative? In my actual dataset I want to drop the groups where the sum or mean is zero.</p>