title: Getting the column names of a Data Frame with sapply
body: <p>I want to get the columns names of a Data Frame with the following code: </p>
  
  <pre><code>DF &lt;- data.frame(X=c(1,2), Y=c(3,4))
  as.character(sapply(DF, names))
  </code></pre>
  
  <p>I've got the following: </p>
  
  <pre><code>"NULL" "NULL"
  </code></pre>
  
  <p>but I need the following result: </p>
  
  <pre><code>"X" "Y" 
  </code></pre>
  
  <p>How can I do this, thanks in advance. </p>