st: Taking random samples from data

["Song" <raravise@gmail.com>]

Hi All,

I have a question about taking random samples from my data. My dataset has 
around 12,500 user ID's with 200,000 observations total and I want to take 
around 500-600 (number of users) random samples. The problem is that each 
member has multiple observations and I want to take all sub-observations for 
each member. Each ID has 4 to 21 observations. For example, if ID number 5 
has 10 observations, I want to take all 10 observations given ID number 5 is 
included in the sample.

I tried the following and ended up with 580 number of users with around 
8,800 observations. This method works, but I wonder if there is there any 
better way for this job, because I have to drop duplicated samples with this 
method.

gen idcnt=_N
bsample 600, cluster(id)     /* sampling with replacement: I do not know how 
to take cluster samples without replacement. */
bysort id: egen idcount=count(id)
compare idcount idcnt
duplicates tag, gen(dup)
drop if dup==1                /* To drop duplicated samples */

I would greatly appreciate your help.
Reo. 
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/