title: split function in xts
body: <p>I don't understand why split applied to xts gives a list of lists. It should return xts objects. Is there something I am missing?</p>
  
  <pre><code>data(sample_matrix)
  x &lt;- as.xts(sample_matrix)
  spl&lt;-split(x, f="days")
  class(spl)
   [1] "list"
  class(spl[1])
   [1] "list"
  class(x)
   [1] "xts" "zoo"
  </code></pre>
  
  <p>Edit: I want to rebuild the xts, with a new field I calculated after splitting it into days. The problem is that now my calculations are in the "split" format, that is in a list of list. How can I "rebuild" a xts from the list of list?</p>