title: Union of dataframes in R by rownames
body: <p>I have 4 dataframes, each the index in a list. I would like to combine them altogether as one dataframe. In set language from mathematics, it would make most sense for this to be the union on the rownames. So I might have something like this:</p>
  
  <pre><code>U &lt;- union(dfSub[[1]], dfSub[[2]], dfSub[[3]], dfSub[[4]])
  </code></pre>
  
  <p>The problem with the <code>union</code> function is that it operates only on vectors. How can I get this to work on dataframes?</p>
  
  <ol>
  <li>How can I translate this into R?</li>
  <li>Is there a better way of achieving the desired result?</li>
  </ol>
  
  <p><strong>EDIT:</strong> How can I preserve rownames after the union?</p>