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Posts: 39

# Add X days to each subsequent each row, by group

Hi everyone,

I am stuck on a data management task and thought someone here may be able to help me.

I am working with a dataset where each individual has ~30 rows of repeated data. The variables with information that differs are dates and a variable that indicates the first for each group. I'd like to add 7 number of days to every row, by group. I have a start date for the first row for each individual and need to add 7 days to each row until the next individual is reached (e.g., row 31) where the same process is repeated. Any suggestions? Here is what I have and what i want the data to look like. Thank you!!

```data have;
input id date first;
datalines;
1 03OCT2010 1
1         . 0
1         . 0
1         . 0
2 01JAN2011 1
2         . 0
2         . 0
;
run;

data want;
input id date first;
datalines;
1 03OCT2010 1
1 10OCT2010 0
1 17OCT2010 0
1 24OCT2010 0
2 01JAN2011 1
2 08JAN2011 0
2 15JAN2011 0
;
run; ```

Accepted Solutions
Solution
‎09-22-2017 11:22 AM
Posts: 1,389

## Re: Add X days to each subsequent each row, by group

Posted in reply to pamplemouse22

As long as FLAG=1 for the first record of each id, this will work:

``````data want;
set have;
retain tmpdate 0;
tmpdate=ifn(flag=1,date,tmpdate+7);
if flag^=1 then date=tmpdate;
drop tmpdate;
run;``````

All Replies
Solution
‎09-22-2017 11:22 AM
Posts: 1,389

## Re: Add X days to each subsequent each row, by group

Posted in reply to pamplemouse22

As long as FLAG=1 for the first record of each id, this will work:

``````data want;
set have;
retain tmpdate 0;
tmpdate=ifn(flag=1,date,tmpdate+7);
if flag^=1 then date=tmpdate;
drop tmpdate;
run;``````
Contributor
Posts: 39

## Re: Add X days to each subsequent each row, by group

This works beautifully! Thank you.

I'm trying to understand how this works.

What does the carrot in following line do?

``flag^=1``

Super User
Posts: 13,913

## Re: Add X days to each subsequent each row, by group

Posted in reply to pamplemouse22

pamplemouse22 wrote:

This works beautifully! Thank you.

I'm trying to understand how this works.

What does the carrot in following line do?

``flag^=1``

^=   is "not equal" . There are some other ways depending on different keyboards/operating systems that are also acceptable.

so

Flag not equal to 1

Contributor
Posts: 39

## Re: Add X days to each subsequent each row, by group

oh, hah! that makes sense. thank you!

☑ This topic is solved.

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