title: Undesirable result when cutting by year in R
body: <p>There is an undesirable feature in function <code>cut.Date</code>, which when applied on Dec 31 will add next year as a level:</p>
  
  <pre><code>cut(as.Date("2013-12-31"), "year")
  [1] 2013-01-01
  Levels: 2013-01-01 2014-01-01
  </code></pre>
  
  <p>This causes me a lot of troubles when processing data later, I wonder whether there is any alternative to cut data by year without this weird feature?</p>