st: Compute a summary variable based on a predefined algorithm

["Shuaib Kauchali" <sk041123@aol.com>]

Dear subscribers,

Thanks for taking my query.

I have data set of birth cohort data with longitudinal follow-up of these  
children till they were 9months old (270days), unless they were lost to  
follow up or died before then.

the data structure looks like this:
Childid (repeated group variable, daily visit to the clinic)
day (day of visit)
v1 (diarrhea on that day of visit)
v2 <--this is the variable I would like to get(defined as diarrhea  
episodes: a string of 1's separated by at least 3 consecutive 0's is an  
episode)


childid day v1  v2  
1   1   .   .       
1   2   .   .           
1   3   .   .   
1   4   .   .   
2   1   0   1
2   2   1   1
2   3   1   1
2   4   0   1
3   1   1   2
3   2   1   2
3   3   0   2
3   4   0   2
3   5   0   2
3   6   1   2
3   7   1   2
4   1   1   1
4   2   .   1
4   3   1   1
4   4   0   1
4   5   .   1
4   6   0   1
4   7   0   1
5   1   0   1
5   2   1   1
5   3   0   1
5   4   1   1
6   1   0   0
6   2   0   0
6   3   0   0
6   4   0   0
6   5   0   0
6   6   0   0
6   7   0   0


Note:
1. childid=4 is a bit tricky because of missing values; we assume the  
episode to be one as there were not more than 3 days separating 2 events.
2. childid=1 has not had any visits recorded, so he gets missing values  
for v2.
3. not everyone is followed-up for the same period: loss to follow-up,  
death, or completed the study (in my data set this should happen when the  
child reaches 270 days from birth. This is a birth cohort of 2500 children)

My problem is I am unable to manipulate the data in Stata to get me the  
summary v2 of the number of episodes of diarrhea per child by total number  
of days observed. I am new to stata, but have been am a good learner (I  
have many of the stata press books to help). One way I came across in the  
books was to use explicit subscriptiing; this would allow me to count the  
total number of days followed per child; but I ma not sure how to create  
the alogorithm for the v2 creation--perhaps foreach, forvalue, or even  
while, local macro???. I find the commands a bit intimidating for a  
newcomer, but am willing to spend time learning it.

Can anyone help?
Best wishes

Shuaib


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