title: How to Parse Year + Week Number in R?
body: <p>Is there a good way to get a year + week number converted a date in R? I have tried the following:</p>
  
  <pre><code>&gt; as.POSIXct("2008 41", format="%Y %U")
  [1] "2008-02-21 EST"
  &gt; as.POSIXct("2008 42", format="%Y %U")
  [1] "2008-02-21 EST"
  </code></pre>
  
  <p>According to <code>?strftime</code>:</p>
  
  <blockquote>
    <p>%Y Year with century. Note that whereas there was no zero in the
    original Gregorian calendar, ISO 8601:2004 defines it to be valid
    (interpreted as 1BC): see <a href="http://en.wikipedia.org/wiki/0_(year)" rel="noreferrer">http://en.wikipedia.org/wiki/0_(year)</a>. Note
    that the standard also says that years before 1582 in its calendar
    should only be used with agreement of the parties involved.</p>
    
    <p>%U Week of the year as decimal number (00–53) using Sunday as the
    first day 1 of the week (and typically with the first Sunday of the
    year as day 1 of week 1). The US convention.</p>
  </blockquote>