title: Subsetting winter (Dez, Jan, Feb) from daily time series (zoo)
body: <p>I have a daily zoo (xts) with a few decades of data in the following format:  </p>
  
  <pre><code>head(almorol)
  1973-10-02 1973-10-03 1973-10-04 1973-10-05 1973-10-06 1973-10-07
       183.9      208.2      153.7       84.8       52.5       35.5
  </code></pre>
  
  <p>and I would like to plot just winter data (the full months of December, January and February). I found the subsetting for xts so I thought I could extract all the Decembers using: </p>
  
  <pre><code>x&lt;-apply.yearly(almorol, FUN=last(almorol, "1 month"))
  </code></pre>
  
  <p>and then do something similar for Jan and Feb, but I get the following error:  </p>
  
  <pre><code>Error in get(as.character(FUN), mode = "function", envir = envir) :
  object 'FUN' of mode 'function' was not found
  </code></pre>
  
  <p>I can use the <code>apply.yearly</code> and <code>last(almorol, "1 month")</code> separately but when I combine them it doesn't work.  Does anyone know a way of subsetting those 3 months of the time series? Thanks for helping!</p>