R help - Nov 2000 - Randomly selecting n (unique) elements out of vector of length m...

Dear R users,

I wonder if there is a simple way to select a random and non-overlapping
subset of a vector?
Say, I need to randomly select 10 out of 100 numbers in a vector V. By
"non-overlapping" I
mean that a number in any position in V (V[1]...V[100]) should be
selected at most once
(i.e. selection without recycling).

I could simplu use a uniform distribution to generate selection indices:
> floor( runif(10, min=1, max=101) )
 [1] 17 34 16 91 43  2 22 75 59 38

but there is no guarantee that elements will be unique, so I'll have to
check and add some if
needed (and probably do it a few times)...

Is there a simper way?

Thanks,
Aleksey

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On Thu, Nov 16, 2000 at 08:01:23PM -0500, Aleksey Naumov
wrote:
> Dear R users,
> 
> I wonder if there is a simple way to select a random and non-overlapping
> subset of a vector?
> Say, I need to randomly select 10 out of 100 numbers in a vector V. By
> "non-overlapping" I
> mean that a number in any position in V (V[1]...V[100]) should be
> selected at most once
> (i.e. selection without recycling).
> 
> I could simplu use a uniform distribution to generate selection indices:
> 
> > floor( runif(10, min=1, max=101) )
>  [1] 17 34 16 91 43  2 22 75 59 38
> 
> but there is no guarantee that elements will be unique, so I'll have to
> check and add some if
> needed (and probably do it a few times)...
> 
> Is there a simper way?
> sample(1:101, 10, replace=FALSE)
 [1] 77 56 84  6  2 50 63 99 35 11

	Ross
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Thank you all very much! The answer was simple, but it just wasn't clear
where to
look for it
(I checked in "Keywords by Topic", "An Introduction to R",
and "Reference Manual")

:-)

Aleksey

-------
Try the function sample().  In your case...
  subset <- sample(V,size=10,replace=FALSE)

Cheers, Pierre


Aleksey Naumov wrote:
> Dear R users,
>
> I wonder if there is a simple way to select a random and non-overlapping
> subset of a vector?
> Say, I need to randomly select 10 out of 100 numbers in a vector V. By
> "non-overlapping" I
> mean that a number in any position in V (V[1]...V[100]) should be
> selected at most once
> (i.e. selection without recycling).
>
> I could simplu use a uniform distribution to generate selection indices:
>
> > floor( runif(10, min=1, max=101) )
>  [1] 17 34 16 91 43  2 22 75 59 38
>
> but there is no guarantee that elements will be unique, so I'll have to
> check and add some if
> needed (and probably do it a few times)...
>
> Is there a simper way?
>
> Thanks,
> Aleksey
>
>
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> r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
> Send "info", "help", or "[un]subscribe"
> (in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
>
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