title: From number to formatted datetime in R
body: <p>I have a field into a dataframe of class numeric.
  I want to convert that into a date time format.</p>
  
  <p>value: 1353959527000000
  expected: 2012-11-26 11:52:07.000-08:00</p>
  
  <p><strong>How do I do that in R?</strong></p>
  
  <p>I tried:
  Using lubridate or default Posix conversion and nothing produced the date above. Read a bunch of posts and still not figuring out what I am doing wrong.</p>
  
  <pre><code>dn &lt;- 1353959527000000 
  as.POSIXct(as.numeric(as.character(dn)),origin="1970-01-01 00:00:00")
  </code></pre>
  
  <p>output was something super off the expected date with some gibberish.
  Same output trying this</p>
  
  <pre><code>as_datetime(1353959527000000, origin = "1970-01-01 00:00:00")
  </code></pre>