[R] Generate N random numbers with a given probability and condition

[Bert Gunter]

You need to heed Rolf's advice.

N random integers by definition cannot have a fixed sum.

Cheers,
Bert



Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Tue, Jul 10, 2018 at 5:11 PM, Nelly Reduan <nell.redu using hotmail.fr> wrote:

> Thank you very much for your reply.
>
>
> By omitting the probability, the expected results could be:
>
>
> c(2, 0, 0, 0, 0, 0, 1, 0, 5, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0)
>
>
> c(0, 0, 1, 0, 0, 1, 1, 0, 6, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0)
>
>
> If I omit the probability, I would like to generate N random positive
> integers that sum to M and the integers would be selected from a uniform
> distribution.
>
>
> Many thanks for your time
>
> Nell
>
>
> ________________________________
> De : Rolf Turner <r.turner using auckland.ac.nz>
> Envoyé : mercredi 4 juillet 2018 16:11:11
> À : Nelly Reduan
> Cc : r-help using r-project.org
> Objet : Re: [R] Generate N random numbers with a given probability and
> condition
>
>
> On 05/07/18 10:21, Nelly Reduan wrote:
>
> > Dear all,
> >
> > I would like to generate N random numbers with a given probability and
> condition but I'm not sure how to do this.
> > For example, I have N = 20 and the vector from which to choose is seq(0,
> 10, 1). I have tested:
> >
> > x <- sample(seq(0, 10, 1), 20, replace=TRUE, prob=rep(0.28,
> times=length(seq(0, 10, 1))))
> >
> > But I don�t know how to put the condition sum(x) <= max(seq(0, 10, 1)).
> > Many thanks for your time.
>
> Your thinking requires considerable clarification.
>
> (1) Note that seq(0,10,1) is just 0, 1, 2, ..., 10.
>
> (2) Hence length(seq(0,10,1)) is 11.
>
> (3) Likewise max(seq(0,10,1)) is 10.
>
> (4) Your prob vector is *constant* --- so specifying "prob" makes
>      no difference --- the result is the same as if you omitted "prob".
>
> (5) You need to think carefully about what you really mean by "random".
>      In what way do you want the final result to be "random"?
>
> I expect that the lecturer who assigned this problem to you  needs to
> clarify his/her thinking as well.
>
> cheers,
>
> Rolf Turner
>
> --
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
>
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>
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