title: rbind.xts from list of xts objects
body: <p>I have a list of xts objects that have index and column names in common. </p>
  
  <p>I want to rbind by index and average the columns : </p>
  
  <pre><code>dts = seq.POSIXt(from = Sys.time() - days(2), to = Sys.time(), by = 'day')
  x1 = xts(x = 1:3, order.by = dts)
  names(x1) = 'a'
  x2 = xts(x = 2:4, order.by = dts)
  names(x2) = 'a'
  
  x = rbind.xts(x1, x2)  
  aggregate(x, index(x), 'mean')
  </code></pre>
  
  <p>This works well for what I want, the issue is that the xts objects are stored in a list and not as seperate objects. </p>
  
  <p>If I try </p>
  
  <pre><code>rbind.xts(list(x1, x2))
  </code></pre>
  
  <p>They don't join: </p>
  
  <pre><code>[[1]]
                      a
  2020-04-04 15:17:42 1
  2020-04-05 15:17:42 2
  2020-04-06 15:17:42 3
  
  [[2]]
                      a
  2020-04-04 15:17:42 2
  2020-04-05 15:17:42 3
  2020-04-06 15:17:42 4
  </code></pre>
  
  <p>How can I rbind from a list?</p>