Calculating difference between consecutive rows

[BayzidurRahman]

I want to calculate difference in dates in consecutive rows by the ID variable. That is, for the first occurrence of the ID value the difference should be missing. I tried with the following code with no luck.

data date;
   input ID DATE;
   format date date10.;
datalines;
1	44562
1	44563
1	44564
1	44583
1	44584
1	44585
1	44586
2	44960
2	44961
2	44962
2	44963
2	44964
2	44965
2	44966
2	44972
2	44973
3	44974
3	44975
3	44976
3	44977
3	44978
3	44979
;
run;

data date1;
set date;
by id;
difference=dif(date); run;

[PaigeMiller]

data date1;
   set date;
   by id;
   if first.id then difference=.;
   else difference=dif(date); 
run;

[BayzidurRahman]

It didn't work.

Obs ID DATE difference 
1 1 02JAN2082 . 
2 1 03JAN2082 . 
3 1 04JAN2082 1 
4 1 23JAN2082 19 
5 1 24JAN2082 1 
6 1 25JAN2082 1 
7 1 26JAN2082 1 
8 2 04FEB2083 . 
9 2 05FEB2083 375 
10 2 06FEB2083 1 
11 2 07FEB2083 1 
12 2 08FEB2083 1 
13 2 09FEB2083 1 
14 2 10FEB2083 1 
15 2 16FEB2083 6 
16 2 17FEB2083 1 
17 3 18FEB2083 . 
18 3 19FEB2083 2 
19 3 20FEB2083 1 
20 3 21FEB2083 1 
21 3 22FEB2083 1 
22 3 23FEB2083 1 

[PaigeMiller · Accepted solution]

data date1;
   set date;
   by id;
   difference=dif(date); 
   if first.id then difference=.;
run;

[BayzidurRahman]

Thanks.