title: Adding additional observation in panel data in R
body: <p>I am trying to add additional years to my panel data.  Just wondering if you guys have any ideas of quick way of doing it.  Keep in mind my real data is T=6, i=4000.  </p>
  
  <pre><code># Here is my input
  data = data.frame(time=c(30,40,50,30,40,50,30,40,50), 
                    id=c(1,1,1,2,2,2,3,3,3), 
                    d=c(1,4,7,8,14,2,41,11,61))
  # declare panel data individ and time
  pd = pdata.frame(data, c("id","time"), drop.index=FALSE)
  
  #this is what I want out... 
  data.out = data.frame(time=c(30,40,50,60,30,40,50,60,30,40,50,60), 
                        id=c(1,1,1,1,2,2,2,2,3,3,3,3), 
                        d=c(1,4,7,8,9,14,2,41,50,11,61,70))
  # declare panel data individ and time
  pd.data.out = pdata.frame(data.out, c("id","time"), drop.index=FALSE)    
  </code></pre>