title: Adding two data-frames with different values in a common column
body: <p>I have two data frames. I need to add them to calculate the total number of matches played and perform further calculations from the answer. But every time I try to add them, some of the rows have Nan values. </p>
  
  <p><a href="https://i.stack.imgur.com/t2OuJ.png" rel="nofollow noreferrer">Image of the two given dataframes</a></p>
  
  <p>The result of adding them comes out like this</p>
  
  <p><a href="https://i.stack.imgur.com/Sspuv.png" rel="nofollow noreferrer">Image of the output on adding the two dataframes</a></p>
  
  <p>How do I add them without getting NaN values???</p>