title: Count words in a dataframe column
body: <p>I have a dataframe with sentences in the first column and I want to count the words in it :</p>
  
  <p>Input :</p>
  
  <pre><code>Foo bar
  bar example
  lalala foo
  example sentence foo
  </code></pre>
  
  <p>Output :</p>
  
  <pre><code>foo       3
  bar       2
  example   2
  lalala    1
  sentence  1
  </code></pre>
  
  <p>Is there a simple way to do this ? </p>
  
  <p>If not, how should I do it ? I see two ways :</p>
  
  <pre><code>Append all the sentences in one huge string
  And then count the words somehow
  </code></pre>
  
  <p>(seems very inefficient)
  Or </p>
  
  <pre><code>Split the column in multiple columns on spaces " " (I know there's a package for that, can't remember which one)
  And then rbind each columns into one
  </code></pre>