st: Creating variable based on time reference

[Mathew Kiang <mathew.kiang@gmail.com>]

I have a data set with 3 variables -- "id", "datesubmitted", and "group" 
-- and 5 observations.

id    datesubmitted    group
1.    1oct2011    1
2.    1aug2011    2
3.    2aug2011    2
4.    5aug2011    2
5.    9oct2011    1

I would like to create a new variable called "responsetime" which 
reflect the amount of time elapsed (categorically) between the first 
response and each later observation within a group. For example, if an 
observation occurred within two days of the first response from that 
group, it would be a 1; between two and five days, it would be a 2; six 
and greater would be a 3. In this case, IDs 1 and 5 would have a 
"responsetime" of 1 and 3, respectively. IDs 2, 3, and 4 would have 
"responsetime" of 1, 1, and 2, respectively.

I'd like to do this across thousands of observations and dozens of 
groups. Is there a simple way to do this that the trusty Google didn't 
turn up?

Any help is appreciated.

Thanks,
Matt

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