title: Melt the Upper Triangular Matrix of a Pandas Dataframe
body: <p>Given a square pandas DataFrame of the following form:</p>
  <pre><code>   a  b  c
  a  1 .5 .3
  b .5  1 .4
  c .3 .4  1
  </code></pre>
  <p>How can the <a href="http://mathworld.wolfram.com/UpperTriangularMatrix.html" rel="noreferrer">upper triangle</a> be melted to get a matrix of the following form</p>
  <pre><code> Row     Column    Value
    a        a       1
    a        b       .5 
    a        c       .3
    b        b       1
    b        c       .4
    c        c       1 
  
  #Note the combination a,b is only listed once.  There is no b,a listing     
  </code></pre>
  <p>I'm more interested in an idiomatic pandas solution, a custom indexer would be easy enough to write by hand...</p>
  <p>Thank you in advance for your consideration and response.</p>