title: Python: creating categorical variable in the existing column
body: <p>I have a DataFrame in python that has a column holding difference of 2 dates. I would like to create a new/overwrite on the existing column that can convert numeric to categorical variable based on below rules:</p>
  
  <pre><code>difference              0 days    Level 0
  difference              2 days    Level 1
  difference              2-6 days  Level 2
  difference             6-15 days  Level 3
  difference             15-69 days Level 4
  difference             NAT        Level 5
  </code></pre>
  
  <p>how this could be accomplished.</p>