title: cbind() time series without NAs
body: <p>I've observed that for many operators on overlapping time series, the result is given only for the overlapping portion, which is nice:</p>
  
  <pre><code>&gt; (ts1 &lt;- ts(1:5, start=1, freq=3))
  Time Series:
  Start = c(1, 1) 
  End = c(2, 2) 
  Frequency = 3 
  [1] 1 2 3 4 5
  &gt; (ts2 &lt;- ts((7:3)^2, start=2, freq=3))
  Time Series:
  Start = c(2, 1) 
  End = c(3, 2) 
  Frequency = 3 
  [1] 49 36 25 16  9
  &gt; ts1 + ts2
  Time Series:
  Start = c(2, 1) 
  End = c(2, 2) 
  Frequency = 3 
  [1] 53 41
  </code></pre>
  
  <p>However, this doesn't seem to be the case with <code>cbind()</code>.  While the output is aligned properly, <code>NA</code>s are created for the non-overlapping data:</p>
  
  <pre><code>&gt; (mts &lt;- cbind(ts1, ts2))
  Time Series:
  Start = c(1, 1) 
  End = c(3, 2) 
  Frequency = 3 
           ts1 ts2
  1.000000   1  NA
  1.333333   2  NA
  1.666667   3  NA
  2.000000   4  49
  2.333333   5  36
  2.666667  NA  25
  3.000000  NA  16
  3.333333  NA   9
  </code></pre>
  
  <p>Is there a way to perform that <code>cbind()</code> without creating the rows with <code>NA</code> in them?  Or if not, what's a good way to take the result and strip off the rows with the <code>NA</code>s?  It's not a simple matter of subscripting, because then it loses its timeseries nature:</p>
  
  <pre><code>&gt; mts[complete.cases(mts),]
       ts1 ts2
  [1,]   4  49
  [2,]   5  36
  </code></pre>
  
  <p>Maybe something with <code>window()</code>, but calculating the start &amp; end times for the window seems a little yucky.  Any advice is welcome.</p>