title: Selecting columns/axes for correlation from Pandas df
body: <p>I have a pandas dataframe like the one below. I would like to build a correlation matrix that establishes the relationship between product ownership and the profit/cost/rev for a series of customer records.</p>
  
  <pre><code>    prod_owned_a    prod_owned_b    profit      cost    rev
  0   1               0               100         75      175
  1   0               1               125         100     225
  2   1               0               100         75      175
  3   1               1               225         175     400
  4   0               1               125         100     225
  </code></pre>
  
  <p>Ideally, the matrix will have all prod_owned along one axis with profit/cost/rev along another. I would like to avoid including the correlation between prod_owned_a and prod_owned_b in the correlation matrix.</p>
  
  <p>Question: How can I select specific columns for each axis? Thank you!</p>