[R] Random # generator accuracy

[Jim Bouldin]

Dan Nordlund wrote:

"It would be necessary to see the code for your 'brief test' before anyone
could meaningfully comment on your results.  But your results for a single
test could have been a valid "random" result."

I've re-created what I did below.  The problem appears to be with the
weighting process: the unweighted sample came out much closer to the actual
than the weighted sample (>1% error) did.  Comments?
Jim

> x
 [1]  1  2  3  4  5  6  7  8  9 10 11 12
> weights
 [1] 1 1 1 1 1 1 2 2 2 2 2 2

> a = mean(replicate(1000000,(sample(x, 3, prob = weights))));a  # (1
million samples from x, of size 3, weighted by "weights"; the mean should
be 7.50)
[1] 7.406977
> 7.406977/7.5
[1] 0.987597

> b = mean(replicate(1000000,(sample(x, 3))));b  # (1 million samples from
x, of size 3, not weighted this time; the mean should be 6.50)
[1] 6.501477
> 6.501477/6.5
[1] 1.000227


Jim Bouldin, PhD
Research Ecologist
Department of Plant Sciences, UC Davis
Davis CA, 95616
530-554-1740