# Re: st: How to sample uniformly over a set of specific observations?

 From "Svend Juul" To Subject Re: st: How to sample uniformly over a set of specific observations? Date Sun, 14 Oct 2007 21:03:34 +0200

```Tiago wrote:

Suppose I have the following data set:

var1 var2 var3
0.5 0.5 0.25
0.4 0.4 0.16
0.3 0.4 0.12
0.8 0.4 0.32
0.4 0.2 0.08

In this sense, I would like to generate a new variable, say var4, which
may take one out of the 5 values presented (with equal probabilities).
I could not think about an easy way to do that using Stata when I have
several observations and, in some cases, repeated observations as well.

--------------------------------------------------

With three candidate variables:

set seed 12345          // if you need to reproduce exactly
generate x = uniform()
generate var4 = var1
replace var4 = var2 if x > 1/3
replace var4 = var3 if x > 2/3

But you write about "the 5 values presented". You have five observations;
three values per obervation, but 15 values in total. So I am not quite
sure what you are looking for.

Hope this helps, anyway.

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, work:  +45 8942 6090
Phone, home:  +45 8693 7796
Fax:          +45 8613 1580
E-mail:       sj@soci.au.dk
_________________________________________________________

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