title: dask dataframe drop duplicate index values
body: <p>I am using dask dataframe with python 2.7 and want to drop duplicated index values from my df. </p>
  
  <p>When using pandas i would use </p>
  
  <pre><code>df = df[~df.index.duplicated(keep = "first")]
  </code></pre>
  
  <p>And it works </p>
  
  <p>When trying to do the same with dask dataframe i get </p>
  
  <blockquote>
    <p>AttributeError: 'Index' object has no attribute 'duplicated'</p>
  </blockquote>
  
  <p>I could reset the index and than use the column that was the index to drop duplicated but I would like to avoid it if possible </p>
  
  <p>I could use df.compute() and than drop the duplicated index values but this df is too big for memory. </p>
  
  <p>How can i drop the duplicated index values from my dataframe using dask dataframe?</p>