title: How to remove duplicates within a group in Pandas
body: <p>I am looking to remove duplicates "within" a group. How can I do this in the most efficient way? </p>
  
  <p>I have tried just grouping the data by ID, but since the companies can raise the same type of investment rounds in different years, this approach leads me to a wrong result. </p>
  
  <p>I have data like this:</p>
  
  <pre><code>+----+-----------+-----------+---------------+
  | ID |   Type    | seed_year | series_a_year |
  +----+-----------+-----------+---------------+
  |  1 | seed      |      2014 |             0 |
  |  2 | seed      |      2014 |             0 |
  |  2 | seed      |      2015 |             0 |
  |  3 | seed      |      2012 |             0 |
  |  3 | series_a  |         0 |          2014 |
  |  3 | series_a  |         0 |          2015 |
  +----+-----------+-----------+---------------+
  </code></pre>
  
  <p>Where my desired output would be:</p>
  
  <pre><code>+----+----------+-----------+---------------+
  | ID |   Type   | seed_year | series_a_year |
  +----+----------+-----------+---------------+
  |  1 | seed     |      2014 |             0 |
  |  2 | seed     |      2014 |             0 |
  |  3 | seed     |      2012 |             0 |
  |  3 | series_a |         0 |          2014 |
  +----+----------+-----------+---------------+
  </code></pre>
  
  <p>I would like to keep the first (oldest) funding round.</p>