title: Count occurrences of strings separated by a semicolon
body: <p>I have a .csv file which is a database of articles. Each article has some keywords associated, with the number of keywords being different each time.</p>
  
  <p>Something a bit like this :</p>
  
  <pre><code>article_id,keywords
  1,word1;word2;word3
  2,word1;word4
  3,word2;word3
  </code></pre>
  
  <p>I would like to count how many times each keyword appear in my .csv file, how could I do this? And yes, they are separated by semicolons.</p>
  
  <p>Here is a sample of the .csv :</p>
  
  <pre><code>id,keywords,date,nbComments,nbView,nbStars,nbVotes,source
  44941,Alain Soral;Emmanuel Macron;France;François Fillon;Front national;Mélenchon;Politique,2017-04-04 00:00:00,21,101368,5,688,E&amp;R
  44309,Féminisme;France;François Hollande;Immigration;Internet;Marine Le Pen;Médias;People;Politique;Terrorisme,2017-02-23 00:00:00,30,43908,5,226,ERTV
  45338,Allemagne;France;Histoire;Judaïsme;Médias;Pologne;Seconde Guerre mondiale,2017-04-25 00:00:00,31,24019,4,121,ERTV
  </code></pre>