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st: Re: -Sample-, but each observation has irregular # of rows


From   "Jitian Sheu" <jtsheu@bu.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: -Sample-, but each observation has irregular # of rows
Date   Tue, 25 Nov 2003 21:06:30 -0500

One way to do this is to use the following method:
suppose you only want to sample 100 ids from them(you can easily change the
method to fit your sampling criteria)

sort id
by id: gen n=_n
sort n id
gen tmp=uniform() if n==1
sort  n tmp
gen tmpx=.
by n : replace tmpx=_n
gen    sampledid=1 if n==1& tmpx<=100

gen  xid=.
sort id sampleid
by id: replace xid=sampleid[1]

keep xid==1


this should works


jt

----- Original Message ----- 
From: "Chih-Mao Hsieh" <hsieh@wustl.edu>
To: <statalist@hsphsun2.harvard.edu>
Sent: Tuesday, November 25, 2003 8:37 PM
Subject: st: -Sample-, but each observation has irregular # of rows


> Hello all,
>
>
> I have a dataset from which I have to sample.  For each observation
> ("ID" in table below), there are multiple rows.  And the number of rows
> is irregular per ID.  My problem:  I want to be able to sample ID's from
> the dataset.  Say the dataset has 3 ID's like the following:
>
> ID     x       y      var1    var2
> 001    3       4       5       3
> 001    3       5       7       6
> 001    4       5       2       3
> 002    2       4       1       5
> 003    1       2       9       11
> 003    1       3       6       2
> 003    1       4       9       5
> 003    2       3       10      2
> 003    2       4       7       4
> 003    3       4       6       12
>
> If I sample 1 ID and get #001, I want to get all of #001's 3 rows.  Of
> course, I am aware of the working man's solution: collapse by(id),
> sample, merge back to original, keep _merge==3.  But this seems
> inefficient.  I've searched the Statalist and "search sample" in STATA
> 8, but to no avail.  Is there not an easier way to do what I need?
>
>
> Thanks in advance,
> Chihmao
>
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>

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