title: Linking string tuples to a crosstable dataframe
body: <p>if I have a data frame of :</p>
  
  <pre><code>df1 = matchups 1    matchups 2    matchups 3
        ('a', 'b')    ('b', 'c')    ('a', 'c')
        ('d', 'a')    ('c', 'd')    ('a', 'e')
  </code></pre>
  
  <p>and so on..</p>
  
  <p>and I have a crosstable:</p>
  
  <pre><code>df2 =     a     b     c     d     e
        a  NaN  -1.0  +2.0  -8.0   +5.0
  
        b  +1.0  NaN  +2.5  +3.0    0
  
        c  -2.0 -2.5  NaN   +5.5   -3.5
  
        d  +8.0 -3.0  -5.5  NaN   +2.8
  
        e  -5.0   0   +3.5  -2.8    NaN
  </code></pre>
  
  <p>And I wanted for each matchup to return a value as so</p>
  
  <pre><code>df1 = matchups 1    matchups 2    matchups 3
         +1.0           -2.5         -2.0
         -8.0           -5.5         -5.0
  </code></pre>
  
  <p>I'm having issues referencing to both of the data frames and returning a value. Could someone help me out? Thanks in advance</p>