title: Column name in data frame goes back to numeric
body: <p>Hi I'm trying to load some dates as column names of my data frame but they will only appear as numbers (11595 for example) even if I'm forcing them with as.Date</p>
  
  <p>Is there another way to do this? Thanks!</p>
  
  <pre><code>dates  &lt;-  seq(as.Date("2000-1-1"), as.Date("2018-10-1"),  by="3 months") -1
  d.test &lt;-  data.frame(matrix(0, ncol = 8, nrow = 8))
  
  for (i in 1:8) {
  
    colnames(d.test)[i] &lt;- as.Date(dates[i], "yyyy-mm-dd")
  }
  </code></pre>