[R] Question: reproducibility of random sampling with replacement

[Bert Gunter]

You have to set the same seed before each random number generation!
You did not do this.



Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
H. Gilbert Welch




On Wed, Jan 1, 2014 at 2:12 PM, Chee Chen <chee.chen at yahoo.com> wrote:
> Dear All,
>
> I would like to ask for your help on "reproducibility of random sampling with replacement". For example, one re-samples the rows with replacement of a residual matrix and uses the new residual matrix thus obtained to produce a statistic ; repeat this for a certain number of times.
>
> My questions:  will the above produce ever be reproducible by setting a seed? Namely,  Given the same residual matrix, Ted applies the above process and so does Jack, will they get the same results by setting a seed?
>
> My attempt: setting seed does not freeze the command "sample" from  getting different samples, as from the codes:
> ====
> x= 1:20
> S = matrix(0,5,20)
> for (i in 1:5) {
>   S[i,] = sample(x, replace=FALSE)
> }
>
> set.seed(123)
>
> T = matrix(0,5,20)
> for (i in 1:5) {
>   T[i,] = sample(x, replace=FALSE)
> }
> sum(S==T)
> ===
>
> I would appreciate any comments and/or suggestions on this.
> Regards,
> Chee
>
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>
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