title: Calculate time difference in R
body: <p>I'm currently struggling with R and calculating the time difference in days.</p>
  
  <p>I have data.frame with around 60 000 rows. In this data frame there are two columns called "start" and "end". Both columns contain data in UNIX time format WITH milliseconds - as you can see by the last three digits. </p>
  
  <pre><code>Start &lt;- c("1470581434000", "1470784954000", "1470811368000", "1470764345000") 
  
  End &lt;- c("1470560601000", "1470581549000", "1470785452000", "1470764722000") 
  
  d &lt;- data.frame(Start, End)
  </code></pre>
  
  <p>My desired output should be a extra column called timediff where the time difference is outline in days. </p>
  
  <p>I tried it with timediff and strptime which I found here. But nothing worked out. 
  Maybe one of you worked with calculation of time differences in the past.
  Thanks a lot</p>