How to calculate days between dates in a row

[hjjijkkl]

I have a data that looks like the table below. how do i calculate the number of days between dates in the row by ID 

ID	Date
1	11/20/18
1	11/20/18
1	11/28/18
3	6/4/18
3	6/20/18

I want an output that looks like the table below

ID	Date	DiffDate
1	11/12/18
1	11/20/18	8
1	11/28/18	8
3	6/4/18
3	6/20/18	16

[novinosrin · Accepted solution]

data have;
input 
ID

Date :mmddyy10.;
format date mmddyy10.;
cards;
1

11/12/18

1

11/20/18

1

11/28/18

3

6/4/18

3

6/20/18
;

data want;
 set have;
 by id;
 DiffDate=dif(date);
 if first.id the DiffDate=.;
run;