title: Remove time from XTS
body: <p>I am trying to compare different timeseries, by day.</p>
  
  <p>Currently a typical XTS object looks like:</p>
  
  <pre><code>&gt; vwap.crs
                      QUANTITY QUANTITY.1
  2014-03-03 13:00:00 3423.500     200000
  2014-03-04 17:00:00 3459.941    4010106
  2014-03-05 16:00:00 3510.794    1971234
  2014-03-06 17:00:00 3510.582     185822
  </code></pre>
  
  <p>now, i can strip the time out of the index as follows:</p>
  
  <pre><code>&gt; round(index(vwap.crs),"day")
  [1] "2014-03-04" "2014-03-05" "2014-03-06" "2014-03-07"
  </code></pre>
  
  <p>My question is, how do I replace the existing index in variable <strong><em>vwap.crs</em></strong>, with the rounded output above?</p>
  
  <p>EDIT: to.daily fixed it</p>