title: Remove empty lists in pandas series
body: <p>I have a long series like the following:</p>
  
  <pre><code>series = pd.Series([[(1,2)],[(3,5)],[],[(3,5)]])
  
  In [151]: series
  Out[151]:
  0    [(1, 2)]
  1    [(3, 5)]
  2          []
  3    [(3, 5)]
  dtype: object
  </code></pre>
  
  <p>I want to remove all entries with an empty list. For some reason, boolean indexing does not work.</p>
  
  <p>The following tests both give the same error:</p>
  
  <pre><code>series == [[(1,2)]]
  series == [(1,2)]
  
  ValueError: Arrays were different lengths: 4 vs 1
  </code></pre>
  
  <p>This is very strange, because in the simple example below, indexing works just like above:</p>
  
  <pre><code>In [146]: pd.Series([1,2,3]) == [3]
  Out[146]:
  0    False
  1    False
  2     True
  dtype: bool
  </code></pre>
  
  <p>P.S. ideally, I'd like to split the tuples in the series into a DataFrame of two columns also.</p>