title: How can I add a column to a dataframe with a value conditional on another dataframe?
body: <p>I'm working with two dataframes:</p>
  <p>Dataframe1 looks like:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th style="text-align: left;">user (index)</th>
  <th style="text-align: center;">apples</th>
  <th style="text-align: right;">bananas</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td style="text-align: left;">Pete</td>
  <td style="text-align: center;">4</td>
  <td style="text-align: right;">2</td>
  </tr>
  <tr>
  <td style="text-align: left;">Sara</td>
  <td style="text-align: center;">5</td>
  <td style="text-align: right;">10</td>
  </tr>
  <tr>
  <td style="text-align: left;">Kara</td>
  <td style="text-align: center;">4</td>
  <td style="text-align: right;">2</td>
  </tr>
  <tr>
  <td style="text-align: left;">Tom</td>
  <td style="text-align: center;">3</td>
  <td style="text-align: right;">3</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Dataframe2 looks like:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th style="text-align: left;">index</th>
  <th style="text-align: right;">user</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td style="text-align: left;">1</td>
  <td style="text-align: right;">Pete</td>
  </tr>
  <tr>
  <td style="text-align: left;">2</td>
  <td style="text-align: right;">Sara</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I want to create a new boolean column in dataframe1 that is true if the user is in dataframe 2. So output looks like:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th style="text-align: left;">user</th>
  <th style="text-align: center;">apples</th>
  <th>bananas</th>
  <th>new column</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td style="text-align: left;">Pete</td>
  <td style="text-align: center;">4</td>
  <td>2</td>
  <td>True</td>
  </tr>
  <tr>
  <td style="text-align: left;">Sara</td>
  <td style="text-align: center;">5</td>
  <td>10</td>
  <td>True</td>
  </tr>
  <tr>
  <td style="text-align: left;">Kara</td>
  <td style="text-align: center;">4</td>
  <td>2</td>
  <td>False</td>
  </tr>
  <tr>
  <td style="text-align: left;">Tom</td>
  <td style="text-align: center;">3</td>
  <td>3</td>
  <td>False</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I tried using lambda function but didn't get very far.</p>