title: Efficient way to rbind data.frames with different columns
body: <p>I have a list of data frames with different sets of columns.  I would like to combine them by rows into one data frame. I use <code>plyr::rbind.fill</code> to do that. I am looking for something that would do this more efficiently, but is similar to the answer given <a href="https://stackoverflow.com/questions/17308551/do-callrbind-list-for-uneven-number-of-column">here</a></p>
  
  <pre><code>require(plyr)
  
  set.seed(45)
  sample.fun &lt;- function() {
     nam &lt;- sample(LETTERS, sample(5:15))
     val &lt;- data.frame(matrix(sample(letters, length(nam)*10,replace=TRUE),nrow=10))
     setNames(val, nam)  
  }
  ll &lt;- replicate(1e4, sample.fun())
  rbind.fill(ll)
  </code></pre>