Raoul wrote:
I am trying to get a random sample of 40 subjects from a dataset of a
few hundred subject. This is what I did:
.set seed 12345
.gen random = uniform()
.sort random, stable
.drop if _n>40
For various reasons, it might be that some subjects in the sample are
not suitable for selection and I want to exclude them from the sample
and from the overall dataset.
So I selected another sample, however, when I did that other subjects
were selected as well.
.drop if id == 890800 //subject that wasn't suitable dropped
.set seed 12345
.gen random = uniform()
.sort random, stable
.drop if _n>40
What I want is to keep the original 39 subjects as in the old sample
in and just replace the subject that wasn't suitable. Any suggestions
would be appreciated.
===================================================================
The sequence of events is important; the unwanted observation should
be dropped AFTER the random number generation. Unless you are so
unlucky that the 41st subject is unwanted, too, this should work:
. set seed 12345
. gen random = uniform()
. sort random, stable
. drop if _n>41
. drop if id == 890800 //subject that wasn't suitable dropped
Hope this helps
Svend
__________________________________________
Svend Juul
Institut for Folkesundhed, Afdeling for Epidemiologi
(Institute of Public Health, Department of Epidemiology)
Vennelyst Boulevard 6
DK-8000 Aarhus C, Denmark
Phone: +45 8942 6090
Home: +45 8693 7796
Email: [email protected]
__________________________________________
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