title: Create vector of data frame names from a list of data frames
body: <p>I have a list of data frames, and I want to create a character vector that contains the data frame names that meet a certain criteria.  In this case, I want the names of the data frames that contain at least 1 observation.  I need these names in a vector for use in another function later on.</p>
  
  <p>The list of data frames is created automatically by the split function.  For reproducibility, here's a list of data frames:</p>
  
  <pre><code>df1 &lt;- data.frame(replicate(2,sample(0:1,5,rep=TRUE)))
  df2 &lt;- data.frame(replicate(2,sample(0:1,5,rep=TRUE)))
  df3 &lt;- data.frame(replicate(0,sample(0:1,5,rep=TRUE))) #empty
  
  mylist &lt;- list(df1, df2,df3) #create list of data frames
  
  mylist2 &lt;- mylist[sapply(mylist, function(x) dim(x)[1]) &gt; 0] #subset list so that df's with no observations are dropped
  </code></pre>
  
  <p>Now, what I need is a character vector with the names of the data frames in mylist2.  (In this example, "df1" and "df2".)</p>
  
  <p>Thanks!</p>