title: Looping through pandas and finding row column pairs
body: <p>I can't wrap my head around the best way to accomplish this.</p>
  <p>The visualization below is what I would like to accomplish.  I'm not sure what you would call it exactly but essentially I want to iterate through rows and columns and make a new dataframe with the x, y and then the intercepting point.  Just reshaping the dataframe I don't want to lose any values.</p>
  <p>I'm doing this just to learn Pandas so any help in the right direction of how to think about this/ best way to solve it would be greatly appreciated.</p>
  <pre><code>   1  2  3  
  
  1  10 15 20
  
  2  11 16 21
  
  3  12 17 22
  </code></pre>
  <pre><code>   x  y  z
  
     1  1  10
  
     1  2  15
  
     1  3  20
     
     2  1  11
     
     2  2  16
  
     2  3  21
   
     3  1  12
  
     3  2  17
  
     3  3  22
  
  </code></pre>