title: Issue with decomposing xts objects with R
body: <p>I am unable to figure out with I can't decompose the time series below. Any ideas why ?</p>
  
  <pre><code>data(co2,package = "datasets")
  library(lubridate)
  library(xts)
  plot(co2)#ok
  decompose(co2)# ok
  
  
  my_co2 &lt;- xts(co2,order.by = seq(from=dmy(01011959),to=dmy(01121997),length.out = 468))
  plot(my_co2) 
  </code></pre>
  
  <p><code>my_co2</code> and <code>co2</code> seem to be identical..</p>
  
  <pre><code>decompose(my_co2) #
  </code></pre>
  
  <blockquote>
    <p>Error in decompose(my_co2) : time series has no or less than 2 periods</p>
  </blockquote>
  
  <p>I don't understand why this happens. Any ideas?</p>
  
  <p>EDIT :</p>
  
  <pre><code>my_co2_v2 &lt;- xts(frequency = 12,co2,order.by = seq(from=dmy(01011959),to=dmy(01121997),length.out = 468))
  frequency(my_co2_v2) # still 1 !
  attr(my_co2_v2, 'frequency')&lt;- 12
  frequency(my_co2_v2) # ok, it's 12
  plot(decompose(my_co2_v2)) # still not good
  </code></pre>
  
  <p>you are right <code>plot(decompose(ts(my_co2_v2,frequency = 12)))</code> work, but it seems a little bit twisted. Is there a bug un xts regarding frequency ?</p>