title: How to convert unix timestamp (milliseconds) and timezone in R?
body: <p>I have data which has two columns <code>time</code> and <code>timezone</code> that have the timestamp of events. Examples are:</p>
  
  <pre><code>time               timezone
  1433848856453      10800000
  </code></pre>
  
  <p>It seems like the timestamp has fractional seconds in the information as well. I don't understand the timezone format but it must be an equivalent unix format. I need to preserve the fractional seconds as well. How do I go from that to something like in R?</p>
  
  <pre><code>2015-01-01 13:34:56.45 UTC
  </code></pre>
  
  <p>Note: This human readable date is not the actual converted values of the unix timestamp shown.</p>