How to count consecutive days?

[juliajulia]

Hello,

i have a data set with id and service date and i want to know if each service date are 6 month apart or not. i use the lag function but it give me a weird result. Please help me figure out how this works. thank you so much.

data test1;
set test;
by id;
if first.id then date=.;
else date = lag(servicedate);
format date mmddyy10.;
run;

id	Count	servicedate	year
1	0	11/8/2013	2013
1	20	11/7/2014	2014
1	20	2/2/2015	2015
1	20	4/23/2015	2015
1	0	10/8/2015	2015
1	0	1/5/2016	2016
1	20	4/6/2016	2016
1	40	6/30/2016	2016
2	20	8/21/2015	2015
2	20	8/21/2015	2015

[PaigeMiller]

data test1;
set test;
by id;
prev_date=lag(servicedate);
if first.id then date=.;
else date = prev_date;
format date mmddyy10.;
run;

[juliajulia]

Thanks.

i found my question is more complicated than i thought. i actually need to find those dates that has 6 month or greater interval with any of the previous date value. for example,  the value of the newDate variable only keep those dates that have 6 month or greater than any of the previous dates in the servicedate.  How to create the newDate variable? please help.

ID	servicedate	NewDate
1	11/8/2013	11/8/2013
1	12/7/2013
1	2/2/2014	2/2/2014
1	4/23/2014
1	9/8/2014	9/8/2014
1	12/5/2014
1	4/6/2015	4/6/2015
2	3/17/2016	3/17/2016
2	4/17/2016
2	9/18/2016	9/18/2016
2	12/5/2016
2	12/9/2016
2	4/9/2016	4/9/2016
2	11/21/2016	11/21/2016
2	11/21/2016

[andreas_lds]

Sorry, but i can't understand the logic you have described. Why is "4/23/2014" not in the NewDate variable? There are observations with id=1 having a difference of more than six months-

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@juliajulia wrote:

Thanks.

i found my question is more complicated than i thought. i actually need to find those dates that has 6 month or greater interval with any of the previous date value. for example,  the value of the newDate variable only keep those dates that have 6 month or greater than any of the previous dates in the servicedate.  How to create the newDate variable? please help.

ID	servicedate	NewDate
1	11/8/2013	11/8/2013
1	12/7/2013
1	2/2/2014	2/2/2014
1	4/23/2014
1	9/8/2014	9/8/2014
1	12/5/2014
1	4/6/2015	4/6/2015
2	3/17/2016	3/17/2016
2	4/17/2016
2	9/18/2016	9/18/2016
2	12/5/2016
2	12/9/2016
2	4/9/2016	4/9/2016
2	11/21/2016	11/21/2016
2	11/21/2016

---

[PaigeMiller]

data test1;
    set test;
    by id;
    prev_date=lag(servicedate);
    if not first.id and intck('month',prev_date,servicedate,'c')>=6
        then newdate=date;
    format newdate mmddyy10.;
run;

Use the INTCK function to determine how many months have elapsed between the two dates.

I note, as did @andreas_lds that your word description does not match the output you say you want.