Need to calculate difference between two timestamps for every empid
<p>I have data given to me in excel like this.The data shows different employees calling. An employee might have called more than once on same or different days.</p>

<pre><code>empid       call_time_starts
1234         7/1/16  9:00
5678         7/21/16 0:00
1234         7/19/16 3:00
7687         7/21/16 6:00
1234         7/17/16 6:00
</code></pre>

<p>I want result like</p>

<pre><code>empid       call_time_starts   no._of_days
1234         7/1/16  9:00        
5678         7/21/16 0:00
1234         7/19/16 3:00       18 days
5678         7/28/16 6:00        7 days
</code></pre>

<p>I need to find out the number of days for an empid since the last call.
like 1234 id had called first on 7/1/16 9:00 and is now calling after 18days on
7/19/16 3:00 . I need to find that 18 days. 
I can use r or excel for it.</p>