Finding the Date Difference
<p>I've the following data:</p>

<pre><code>ID GROUP     DATE 
A   GR1   12/01/2013
A   GR1   09/04/2014
A   GR1   01/03/2015
A   GR2   04/04/2015
A   GR2   08/21/2015
A   GR1   01/05/2016
A   GR1   06/28/2016
B   GR2   11/01/2013
B   GR2   06/04/2014
B   GR2   04/15/2015
B   GR3   11/04/2015
B   GR2   03/21/2016
B   GR2   07/05/2016
B   GR1   06/28/2016
C   GR2   01/16/2014
C   GR2   06/04/2014
C   GR2   04/15/2015
C   GR3   11/04/2015
C   GR2   03/21/2016
C   GR2   06/05/2016
C   GR1   06/28/2016
</code></pre>

<p>I want to get the difference the person remained in each group. So the new table will look like the following:</p>

<pre><code>ID GROUP     DATE      Diff
A   GR1   12/01/2013
A   GR1   09/04/2014
A   GR1   01/03/2015    398
A   GR2   04/04/2015
A   GR2   08/21/2015    139
A   GR1   01/05/2016
A   GR1   06/28/2016    175
B   GR2   11/01/2013
B   GR2   06/04/2014
B   GR2   04/15/2015    530
B   GR3   11/04/2015
B   GR2   03/21/2016
B   GR2   07/05/2016    106
B   GR1   06/28/2016
C   GR2   01/16/2014
C   GR2   06/04/2014    
C   GR2   04/15/2015    454
C   GR3   11/04/2015
C   GR2   03/21/2016
C   GR2   01/05/2016    76
C   GR1   06/28/2016
</code></pre>

<p>THe value in column "Diff" 398 is coming by taking difference '01/03/2015' - '12/1/2013'. Similarly all other difference.</p>

<p>Now my question is how to get this difference? I can't take max(date)-min(date) at each group, because group are repeating at different period. Similarly I can't take first dot and last dot as in SAS.</p>

<p>I'll be extremely grateful if someone help me with the solution. I would prefer the solution in SAS as the data size is very large. SO will not hold in memory.</p>

<p>Regards,</p>