title: Pandas: Drop consecutive duplicates
body: <p>What's the most efficient way to drop only consecutive duplicates in pandas?</p>
  
  <p>drop_duplicates gives this:</p>
  
  <pre><code>In [3]: a = pandas.Series([1,2,2,3,2], index=[1,2,3,4,5])
  
  In [4]: a.drop_duplicates()
  Out[4]: 
  1    1
  2    2
  4    3
  dtype: int64
  </code></pre>
  
  <p>But I want this:</p>
  
  <pre><code>In [4]: a.something()
  Out[4]: 
  1    1
  2    2
  4    3
  5    2
  dtype: int64
  </code></pre>