title: Creating a new column based on multiple columns from another dataframe
body: <p>I have two dataframes. </p>
  
  <p>The first is individual game data, which looks similar to this:</p>
  
  <pre><code>    Team1 Team2  Team1Score   Team2Score   Year
  0     a     g        100          90       2019
  1     b     h         90         100       2018
  2     c     i         95         105       2017
  3     d     j        100         115       2018
  4     e     k        105         100       2016
  5     f     l        120         130       2015
  6     a     f        100         115       2015 
  </code></pre>
  
  <p>The second is team data for the year, which looks similar to this:</p>
  
  <pre><code>    Team Rating   Year
  0     a     111    2019
  1     g     108    2019
  2     j     105    2018
  3     l      98    2015
  4     b     104    2018
  5     f     120    2015
  6     a     100    2015
  </code></pre>
  
  <p>I want to merge them so that it looks like this:</p>
  
  <pre><code>    Team1 Team2  Team1Score   Team2Score   Year   Team1Rating  Team2Rating
  0     a     g        100          90       2019       111          108
  1     b     h         90         100       2018       104          NULL
  2     c     i         95         105       2017       NULL         NULL
  3     d     j        100         115       2018       NULL         105
  4     e     k        105         100       2016       NULL         NULL
  5     f     l        120         130       2015       120           98
  6     a     f        100         115       2015       100          120
  </code></pre>
  
  <p>I basically want to have the team ratings with the game data. I'm not sure how to approach this and what steps to take</p>