Date difference by group

[mmh]

Hello,
I am a new SAS user.
I want to calculate the date difference by group

I have the following data:

Company_ID Date
1001 05JAN2021
1001 06JAN2021
1001 07JAN2021
1001 08JAN2021
1001 11JAN2021
1002 18FEB2021
1002 21FEB2021
1002 22FEB2021

I want the following output:

Company_ID	Date	Date_Diff
1001	2021-01-05	.
1001	2021-01-06	1
1001	2021-01-07	1
1001	2021-01-08	1
1001	2021-01-11	3
1002	2021-02-18	.
1002	2021-02-21	3
1002	2021-02-22	1

Thank you so much for your kind support!

[Kurt_Bremser · Accepted solution]

Use the DIF function and set a missing value when the group changes:

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

[mmh]

Thank you so much Kurt!
It was really kind of you 🙂
I was just curious. If I wanted to get the difference between months instead, then I should use the following? Or is there a better way?

data want;
set have;
by Company_ID;
mon_diff = intck('month',Date,Date-1);
if first.Company_ID then mon_diff = .;
run;