Re: [R] Odp: how to sample a block

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Mon, 10 Nov 2008 14:05:41 +0100

Petr PIKAL wrote:
> Hi
>
> r-help-bounces@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)]

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.
>>
>> ______________________________________________
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>
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-- 
    O__  ---- Peter Dalgaard             ุster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
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