title: Total unique words in a column - R
body: <p>I am interested in counting unique words that appear in a column. 
  Rather than getting unique words per row as expained in <a href="https://stackoverflow.com/questions/48621428/count-unique-dinstinct-words-into-a-new-column">Count unique/dinstinct words into a new column</a>
  I'm interested in getting one answer which counts all unique entries in that column.
  In the following example the total unique countries are 3: 
  China 
  Australia and 
  Korea</p>
  
  <p>Is there a short way of getting this sum?
  I am still learning R therefore I have limited knowledge.</p>
  
  <pre><code>Countries
  
  China  Australia
  
  Australia
  
  China China 
  
  Korea Korea Korea Korea
  </code></pre>