title: Join comma separated strings in dataframe
body: <p>I have a 3000 cell data frame with cells like this:</p>
  
  <pre><code>['abcd', 'abcd', 'abcd', 'abcd']
  </code></pre>
  
  <p>I want to join the comma separate string into one line without spaces like this:</p>
  
  <pre><code>['abcdabcdabcdabcd']
  </code></pre>
  
  <p>I want to do this for every cell in my data frame</p>