title: subsetting in data.table
body: <p>I am trying to subset a data.table ( from the package <a href="http://cran.r-project.org/web/packages/data.table/index.html">data.table</a> ) in R (not a data.frame).  I have a 4 digit year as a key.  I would like to subset by taking a series of years.  For example, I want to pull all the records that are from 1999, 2000, 2001.  </p>
  
  <p>I have tried passing in my <code>DT[J(year)]</code> binary search syntax the following:</p>
  
  <pre><code>1999,2000,2001
  c(1999,2000,2001)
  1999, 2000, 2001
  </code></pre>
  
  <p>but none of these seem to work.  Anyone know how to do a subset where the years you want to select are not just 1 but multiple years?</p>