title: Pandas, how to filter a df to get unique entries?
body: <p>I have a dataframe like this:</p>
  
  <pre><code>ID  type value
  1   A    8
  2   A    5
  3   B    11
  4   C    12
  5   D    1
  6   D    22
  7   D    13
  </code></pre>
  
  <p>I want to filter the dataframe so that I have a unique occurrence of "type" attrybute (e.g. A appears only once), and if there are more rows that have the same value for "type" I want to choose the one with higher value. 
  I want to get something like:</p>
  
  <pre><code>ID  type value
  1   A    8
  3   B    11
  4   C    12
  6   D    22
  </code></pre>
  
  <p>How do I do this with pandas?</p>