[R] restricted bootstrap

[Prof Brian Ripley]

I see nothing here to do with the 'bootstrap', which is sampling with 
replacement.

Do you know what you mean exactly by 'randomly sample'?  In general the 
way to so this is to sample randomly (uniformly, whatever) and reject 
samples that do not meet your restriction.   For some restrictions there 
are more efficient algorithms, but I don't understand yours.  (What are 
the 'rows'?  Do you want to sample rows in space or xy locations?  How 
come 'dist' is not symmetric?)  For some restrictions, an MCMC sampling 
scheme is needed, the hard-core spatial point process being a related 
example.

On Wed, 3 Sep 2008, Grant Gillis wrote:

> Hello List,
>
> I am not sure that I have the correct terminology here (restricted
> bootstrap) which may be hampering my archive searches.  I have quite a large
> spatially autocorrelated data set.  I have xy coordinates and the
> corresponding pairwise distance matrix (metres) for each row.  I would like
> to randomly sample some number of rows but restricting samples such that the
> distance between them is larger than the threshold of autocorrelation.  I
> have been been unsuccessfully trying to link the 'sample' function to values
> in the distance matrix.
>
> My end goal is to randomly sample M thousand rows of data N thousand times
> calculating linear regression coefficients for each sample but am stuck on
> taking the initial sample. I believe I can figure out the rest.
>
>
> Example Question
>
> I would like to radomly sample 3 rows further but withe the restriction that
> they are greater than 100m apart
>
> example data:
> main data:
>
> y<- c(1, 2, 9, 5, 6)
> x<-c( 1, 3, 5, 7, 9)
> z<-c(2, 4, 6, 8, 10)
> a<-c(3, 9, 6, 4 ,4)
>
> maindata<-cbind(y, x, z, a)
>
>     y x x a
> [1,] 1 1 1 3
> [2,] 2 3 3 9
> [3,] 9 5 5 6
> [4,] 5 7 7 4
> [5,] 6 9 9 4
>
> distance matrix:
> row1<-c(0, 123, 567, 89)
> row2<-c(98, 0, 345, 543)
> row3<-c(765, 90, 0, 987)
> row4<-c(654, 8, 99, 0)
>
> dist<-rbind(row1, row2, row3, row4)
>
>     [,1] [,2] [,3] [,4]
> row1    0  123  567   89
> row2   98    0  345  543
> row3  765   90    0  987
> row4  654    8   99    0
>
> Thanks for all of the help in the past and now
>
> Cheers
> Grant
>
> 	[[alternative HTML version deleted]]
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595