title: Merge xts objects recursively
body: <p>I want to create and merge a number of xts objects </p>
  
  <p>The actual data comes from  a list (where each time series length can vary) and is converted to xts.
  For the sake of reproducibility the problem is similar to the following </p>
  
  <pre><code>x=xts()
  for(i in 1:3){
      n=round(runif(1, 2, 5))
      x=merge(x, x=xts(rnorm(n-1), as.Date(2:n)))
  }
  x
  
  #                       x       x.1        x.2
  # 1970-01-03 01:00:00 0.3130791 0.7817730 0.06623756
  # 1970-01-04 01:00:00        NA 0.4827522 0.94823558
  # 1970-01-05 01:00:00        NA 0.2411705         NA
  </code></pre>
  
  <p>As you see, I need an initial empty xts object to start the recursion. Despite:</p>
  
  <pre><code>xts(1:3, as.Date(1:3))
  #            [,1]
  # 1970-01-02    1
  # 1970-01-03    2
  # 1970-01-04    3
  </code></pre>
  
  <p>when merging generated xts objects with the empty one, the latter is assumed to have a time-based index. </p>
  
  <p>To avoid the time addition, I can create the initial xts item, giving it explicit dummy data. </p>
  
  <pre><code>x= xts(1, as.Date(1))
  for(i in 1:3){
      n=round(runif(1, 2, 5))
      x=merge(x, x=xts(rnorm(n-1), as.Date(2:n)))
  }
  x=x[,-1]
  if(all(is.na(x[1,]))) x=x[-1,]
  x
  #                   x.1         x.2       x.3
  # 1970-01-03 -0.5098130 -0.57121953 -1.259878
  # 1970-01-04 -0.9984952 -0.26467168 -2.413181
  # 1970-01-05  3.0207324 -1.06862153        NA
  # 1970-01-06         NA  0.05542239        NA
  </code></pre>
  
  <p>This works but I have to add extra code for cleaning from the dummy data and most likely, beyond the dummy column, you get also  an extra row for the fake date. </p>
  
  <p>Do you have a cleverer idea to merge recursively xts objects? </p>