title: How to calculate number of words in a string in DataFrame?
body: <p>Suppose we have simple Dataframe</p>
  
  <pre><code>df = pd.DataFrame(['one apple','banana','box of oranges','pile of fruits outside', 'one banana', 'fruits'])
  df.columns = ['fruits']
  </code></pre>
  
  <p>how to calculate number of words in keywords, similar to:</p>
  
  <pre><code>1 word: 2
  2 words: 2
  3 words: 1
  4 words: 1
  </code></pre>