title: Cartesian Product on Pandas Groupby
body: <p>I have a dataframe</p>
  
  <p>df:</p>
  
  <pre><code>col1    col2    col3
  JHGK    B       name1
  JHGK    B       name2
  JHGK    C       name3
  OPDR    B       name4
  ERTH    B       name5
  ERTH    C       name6
  </code></pre>
  
  <p>After doing a groupby on col1, I would like to do cartesian product between( distinct col3 values where col2 = B and distinct col3 values where col2 = C)</p>
  
  <p>Result dataframe:</p>
  
  <p>final:</p>
  
  <pre><code>col1   n1     n2
  JHGK   name1  name3
  JHGK   name2  name3
  ERTH   name5  name6
  </code></pre>