[R] Odp: how to sample a block

[Petr PIKAL]

Peter Dalgaard <p.dalgaard at biostat.ku.dk> napsal dne 10.11.2008 14:05:41:

> Petr PIKAL wrote:
> > Hi
> > 
> > r-help-bounces at r-project.org napsal dne 10.11.2008 13:25:41:
> > 
> >> Hi,
> >> I want to sample a block of information.
> >>
> >> Let's say x is a time series. Using sample(x,5) I get a random sample 
of
> >> length 5 from x.
> >>
> >> Is it possible to sample consecutive observations, i.e. I sample one
> >> observation and also get the next 4 observations?
> > 
> > Easy
> > 
> > sam <-  sample(x,1)
> > x[sam:(sam+4)]
> 
> 
> You mean
> 
> sam <-  sample(seq_along(x),1)
> x[sam:(sam+4)]

Yes, I meant it. Without an example I set my x series as 1:100 so it was 
in seq order and no need to use seq_along.

Petr

> 
> I think this answers the question as posed, but possibly not as meant.
> 
> You might have
> 
> block <- seq_along(x) %/% 5
> 
> and want to an entire block. This is a little more tricky:
> 
> bl <- sample(unique(block),1)
> x[block==bl]
> 
> It gets even trickier if you want to vectorize sampling of multiple 
> blocks, but let's leave that for now.
> 
> > Regards
> > Petr
> > 
> > 
> > 
> >> Thanks a lot!
> >>
> >> Martin
> >> -- 
> >> View this message in context: 
> > http://www.nabble.com/how-to-sample-a-block-
> >> tp20418997p20418997.html
> >> Sent from the R help mailing list archive at Nabble.com.
> >>
> >> ______________________________________________
> >> R-help at r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide 
> > http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> > 
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> 
> 
> -- 
>     O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
>    c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
>   (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 
35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907