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Re: st: Re: reproducing results of a random number generation within a loop using seed


From   Steven Samuels <sjhsamuels@earthlink.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Re: reproducing results of a random number generation within a loop using seed
Date   Mon, 5 May 2008 12:53:18 -0400

-
Take the second -set seed- outside the loop. That will prevent the generation of the same random numbers. I cannot dissect the rest of your code, but it looks like you are generating overlapping pairs in `j': (1,2), (2,3), (3,4). Also, what happens if there is an odd number of observations within a cluster?

Steve

On May 5, 2008, at 12:31 PM, Conner Mullally wrote:


If I can follow up my own question, I looked harder at my
results, and the loop is generating the same two random
numbers for each pair, but it is switching who received
which number within each pair.  Is there anyway I can keep
this from happening?

----- Original Message Follows -----
From: "Conner Mullally" <mullally@primal.ucdavis.edu>
To: statalist@hsphsun2.harvard.edu
Subject: reproducing results of a random number generation
within a loop using seed
Date: Mon, 05 May 2008 10:44:10 -0500

Hello,
I am trying to generate random numbers in a way that can
be replicated later (I am drawing random samples), and
having some trouble. I have two steps in my program. First
, I collapse the data set by group and randomly select
groups using the following code:
collapse $numvarssector, by($cluster)
set seed 54234
generate randomc=uniform()
sort randomc
g id2=_n
g ctreat=.
replace ctreat=1 if id2<=13
replace ctreat=0 if id2>13
sort cluster
drop randomc

I have no problem replicating the results of this step.
Next, after merging the grouped data with the individual
data, so that each person now has a variable "ctreat"
which indicates whether or not he or she is in a treatment
group, I draw random samples from within each treatment
group. What I want to do is the following: order each
observation within the groups by the size of a continuous
variable, "farm." Then, I want to break the observations
into nearest neighbor pairs using this variable, and
randomly assign one person from each pair to the treatment
group: sort cluster farm
by cluster: g id3=_n
sort $cluster id3
g invite=.
levelsof cluster, local(ctlevels)
foreach i of local ctlevels {
qui su id3 if cluster==`i'
forvalues j=1(2)`r(max)' {
set seed 54234
qui generate random`j'`i'=uniform() if
id3==`j'&$cluster==`i'|id3==(`j'+1)&$cluster==`i'
sort random`j'`i'
drop random`j'`i'
qui g d`j'_`i'=_n if
id3==`j'&cluster==`i'|id3==(`j'+1)&cluster==`i'
qui replace invite=1 if d`j'_`i'==1
qui replace invite=0 if d`j'_`i'==2
drop d`j'_`i'
}
}

I get a different sample every time I do this. Note that I
have already dropped the groups with ctreat==0 before
doing this step. Am I setting the seed in the wrong spot?
Or perhaps there is a better way to do this that I am not
seeing...
Thanks in advance
Conner

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