title: Simplest way to extract date from timestamp
body: <p>Consider the following timestamp</p>
  
  <pre><code>timestamp &lt;- ymd_hms("2011-08-10 14:00:00", tz = "Pacific/Auckland")
  
  &gt; timestamp
  [1] "2011-08-10 14:00:00 NZST"
  </code></pre>
  
  <p>What is the simplest way to get the day part <code>2011-08-10</code> from it, and making sure this day is a proper date and not a string?</p>
  
  <p>Using <code>lubridate::day(timestamp)</code> obviously fails here.</p>