[R] Simulation

[gb]

I want to draw a random sample Y_1, ..., Y_n, iid Poisson,
but condition on their sum being equal to  k. Two
suggestions:

1)   lambda <- k / n ## optimal value
     ysum <- -1
     while (ysum != k){
        y <- rpois(n, lambda)
        ysum <- sum(y)
     }
     y

2) Aiming at Multinom(k, 1/n, ..., 1/n):

   y <- as.vector(table(factor(sample(n, k, replace = T), levels = 1:n)))

1) seems to be faster than 2), but my question is whether there is
something even better?  'sample' is fast enough, but how can I do
the rest (factor, table) smarter in 2)?

Thanks for any suggestions!

Göran
-- 
 Göran Broström                      tel: +46 90 786 5223
 professor                           fax: +46 90 786 6614
 Department of Statistics            http://www.stat.umu.se/egna/gb/
 Umeå University
 SE-90187 Umeå, Sweden             e-mail: gb at stat.umu.se

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