title: Transforming a time-series into a data frame and back
body: <p>The output of a time-series looks like a data frame:</p>
  
  <pre><code>ts(rnorm(12*5, 17, 8), start=c(1981,1), frequency = 12)
  
         Jan       Feb       Mar       Apr       May       Jun       Jul     ...
  1981 14.064085 21.664250 14.800249 -5.773095 16.477470  1.129674 16.747669 ...
  1982 23.973620 17.851890 21.387944 28.451552 24.177141 25.212271 19.123179 ...
  1983 19.801210 11.523906  8.103132  9.382778  4.614325 21.751529  9.540851 ...
  1984 15.394517 21.021790 23.115453 12.685093 -2.209352 28.318686 10.159940 ...
  1985 20.708447 13.095117 32.815273  9.393895 19.551045 24.847337 18.703991 ...
  </code></pre>
  
  <p>It would be handy to transform it into a data frame with columns Jan, Feb, Mar... and rows 1981, 1982, ... and then back. What's the most elegant way to do this?</p>