title: Extract year from string and append to dataframe
body: <p>I have a wine dataset with a column called "title" which contains the title of the wine including its vintage year. Refer sample:</p>
  
  <ul>
  <li>Pull 2013 Chardonnay (Paso Robles)</li>
  <li>R2 2013 Camp 4 Vineyard Grenache Blanc (Santa Ynez Valley)</li>
  </ul>
  
  <p>I want to extract just the year in the strings i.e. 2013, and not the rest of the number in the string e.g. 2, 4.</p>
  
  <p>I got to this part:</p>
  
  <h1>Extract vintage year from title column</h1>
  
  <p><code>wine_tidy2$vintage_year &lt;- as.list(str_extract_all(wine_tidy2$title, "[0-9]+"))</code></p>
  
  <p>But how do I exclude other numbers that are not part of the year?</p>
  
  <p>I want to append the result to a data frame. With the above code, it adds the resulting list to the data frame, how can I add to the data frame as another column of integer?</p>
  
  <p>Thank you.</p>