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Finding which seed resulted in a specific sample

3 messages · Isabel Natario, Thierry Onkelinx, Brian Ripley

Isabel Natario
# 
Hello!

I was wanting to find out which random seed could generate the characters
in the word "love", for example, when I sample with replacement from the
vector of the letters. So I've written the code below:

seed=0
set.seed=0
x<-sample(letters,4,replace=T)
while (sum(x==c("l","o","v","e"))<4){
seed<-seed+1
set.seed=seed
x<-sample(letters,4,replace=T)
}

When I run this code I always get that the final x vector is
c("l","o","v","e"), but afterwards, when I try to set.seed iqual to the
value stored in object "seed" I can never reproduce this vector
c("l","o","v","e"), by doing sample(letters,4,replace=T). Why is that?

Thank you very much,

Isabel Natario
--
Dep. Matem?tica
Faculdade de Ci?ncias e Tecnologia
Universidade Nova de Lisboa
2829-516 Caparica, Portugal
icn at fct.unl.pt
Thierry Onkelinx
# 
you need set.seed(seed) instead of set.seed = seed

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to say
what the experiment died of. ~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data. ~ Roger Brinner
The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey

2015-04-13 11:12 GMT+02:00 Isabel Natario <icn at fct.unl.pt>:

  
  


  


      

    

    

      
      

        


  

        

      Brian Ripley
    

    

      
      #
    

  


  

      
On 13/04/2015 10:12, Isabel Natario wrote:

            

      
      
      
    

        
Because you never called the function set.seed(): assigning to a 
variable of that name does not help.

Also, there are far more values of the underlying seed than can be set 
using set.seed(), so this approach will not always work.  However

seed <- 0L
set.seed(seed)
x <- sample(letters,4L,replace=T)
while (sum(x == c("l","o","v","e"))<4L){ # I would have used identical()
   seed <- seed+1L
   set.seed(seed)
   x <- sample(letters,4L,replace=T)
}
seed

gave me an answer (543867)