title: How to combine 2 Date vectors in data frame without changing format
body: <p>I'm trying to put 2 vectors of dates together in one data frame but when I do they change formats.  Any suggestions?</p>
  
  <pre><code>&gt; head(starters)
      [1] "2009-01-02" "2009-02-02" "2009-03-02" "2009-04-01"
      [5] "2009-05-01" "2009-06-01"
      &gt; head(enders)
      [1] "2009-01-30" "2009-02-27" "2009-03-31" "2009-04-30"
      [5] "2009-05-29" "2009-06-30"
      &gt; class(enders)
      [1] "Date"
      &gt; class(starters)
      [1] "Date"
      &gt; comboer &lt;- data.frame(cbind(starters, enders))
      &gt; head(comboer)
        starters enders
      1    14246  14274
      2    14277  14302
      3    14305  14334
      4    14335  14364
      5    14365  14393
      6    14396  14425
  </code></pre>