number of days between dates for column operations

[PatrykSAS]

Hello. I would like to calculate the number of days between dates but for column operations. I have the following data:

ID              DATE

100           2020-07-01

100           2020-07-08

100           2020-07-13

110           2020-06-25

110           2020-06-29

I'd like to achieve data like:

ID              DATE                 DAYS

100           2020-07-01        .

100           2020-07-08        7

100           2020-07-13        5

110           2020-06-25        .

110           2020-06-29        4

Can you help with solution?

[PeterClemmensen · Accepted solution]

data have;
input ID DATE :yymmdd10.;
format date yymmdd10.;
datalines;
100 2020-07-01
100 2020-07-08
100 2020-07-13
110 2020-06-25
110 2020-06-29
;

data want;
   set have;
   by ID;
   days = dif(date);
   if first.ID then days=.;
run;