title: Year Week format R
body: <p>I have a dataframe (df_malaria) with many columns, two of them represent the year and the week of the case.</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>Year</th>
  <th>Week</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2010</td>
  <td>1</td>
  </tr>
  <tr>
  <td>2010</td>
  <td>4</td>
  </tr>
  <tr>
  <td>2010</td>
  <td>5</td>
  </tr>
  <tr>
  <td>2010</td>
  <td>6</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>What i would like to have is an additional column with the date displayed as Year - Week</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>Year-week</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2010 - 01</td>
  </tr>
  <tr>
  <td>2010 - 04</td>
  </tr>
  <tr>
  <td>2010 - 05</td>
  </tr>
  <tr>
  <td>2010 - 06</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I tried to achieve this using the code below but it didnt´t work.</p>
  <pre><code>df_malaria$date &lt;- as.Date(with(df_malaria, paste(Year, Week, sep=&quot;-&quot;)), &quot;%Y-%W&quot;)
  </code></pre>
  <p>Any suggestions?</p>