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


From   "Conner Mullally" <mullally@primal.ucdavis.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: reproducing results of a random number generation within a loop using seed
Date   Mon, 05 May 2008 11:31:02 -0500

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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