title: Rbind does not carry the colnames of a empty data.frame over
body: <p>How to rbind with empty data.frame? It only carries the column names when there is at least one row but not when it is empty.  Empty data.frame is often created before the for loop, so this behavior is annoying. </p>
  
  <p>Example:</p>
  
  <pre><code>test= data.frame(a=1, b=2, c=3)
  rbind(test, c(3,4,5))
    a b c
  1 1 2 3
  2 3 4 5
  test= data.frame(matrix(ncol= 3, nrow= 0))
  names(test) = c("a", "b", "c")
  rbind(test, c(3,4,5))
    X3 X4 X5
  1  3  4  5
  </code></pre>