[R] Odp: how to sample a block

[Peter Dalgaard]

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)]

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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