title: Remove duplicate row, keep first and fill NaN with value from second one
body: <p>I have some duplicate rows in my dataframe, the occurrences have Nan value in specific column 'Rank'. I want to remove duplicate, keep the fisrt occurrence with full data and replace Nan value with value from second occurrence when necessary.</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>Name</th>
  <th>Rank</th>
  <th>City</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>Andre Ryan</td>
  <td>NaN</td>
  <td>London</td>
  </tr>
  <tr>
  <td>Andre Ryan</td>
  <td>86</td>
  <td>Paris</td>
  </tr>
  <tr>
  <td>Paul Nilson</td>
  <td>74</td>
  <td>LA</td>
  </tr>
  <tr>
  <td>Paul Nilson</td>
  <td>NaN</td>
  <td>Chicago</td>
  </tr>
  <tr>
  <td>...</td>
  <td>...-</td>
  <td>...</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>The goal</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>Name</th>
  <th>Rank</th>
  <th>City</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>Andre Ryan</td>
  <td>86</td>
  <td>London</td>
  </tr>
  <tr>
  <td>Paul Nilson</td>
  <td>74</td>
  <td>LA</td>
  </tr>
  <tr>
  <td>...</td>
  <td>...</td>
  <td>...</td>
  </tr>
  </tbody>
  </table>
  </div>