title: Trying to apply regex to a column in a dataframe
body: <p>I have the following df:</p>
  
  <pre><code>               concatenar           buy_sell
  1           BBVA2018-03-2020          sell
  5           santander2018-03-2020      buy
  </code></pre>
  
  <p>I would like to apply regex to the <code>concatenar</code> column, where I would like to display the  <code>[A-Z][a-z]</code> inside that <code>column</code>  values.</p>
  
  <p>This is what I have tried: </p>
  
  <pre><code>re.findall(r'[A-Z][a-z]*',df['concatenar'])
  </code></pre>
  
  <p>But outputs: </p>
  
  <pre><code>TypeError: expected string or bytes-like object
  </code></pre>
  
  <p>My desired output would be :</p>
  
  <pre><code>               concatenar     buy_sell
  1                 BBVA         sell
  5             santander         buy
  </code></pre>
  
  <p>How could I correctly apply the <code>regex</code> to the <code>concatenar</code> column?</p>