Re: [Rd] Cutting up a k-D space (no subject)

From: stefano iacus <jago_at_mclink.it>
Date: Wed 01 Feb 2006 - 18:05:06 GMT

Thanks Brian,
stefano
Il giorno 01/feb/06, alle ore 19:00, Prof Brian Ripley ha scritto:

> Stefano,
>
> Try this
>
> XX <- as.numeric(X[[1]])
> for (i in 2:length(X)) XX <- 10*XX + as.numeric(X[[i]])
> split(seq(along=XX), XX)
>
> You can read off the cell from the decimal expansion of the label.
> And XX goes from observations to cells.
>
> The hard work is done by unique() under the skin (split makes XX
> into a factor).
>
> Brian
>
> On Wed, 1 Feb 2006, stefano iacus wrote:
>
>> Suppose X is a data.frame with n obs and k vars, all variables are
>> factors.
>>
>> tab <- table(X)
>>
>> containes a k-dim array
>>
>> I would like to get a list from tab. This list is such that, each
>> element contain the indexes corresponding to the observations which
>> are in the same cell of this k-dim array. Of course, only for non
>> empty cell.
>>
>> E.g.
>>
>> > set.seed(123)
>> > X <- as.data.frame(matrix(rnorm(5000),100,5))
>> > X$V1 <- cut(X$V1, br=5)
>> > X$V2 <- cut(X$V2, br=5)
>> > X$V3 <- cut(X$V3, br=5)
>> > X$V4 <- cut(X$V4, br=5)
>> > X$V5 <- cut(X$V5, br=5)
>> > tab <- table(X)
>> > which(tab>0) -> cells
>> > length(cells)
>> [1] 94
>>
>> thus, of course, 94 cells over 5^5 = 3125 are non empty.
>> I would like a smart way (without reimplementing table/tabulate) to
>> get the list of length 94 which contains the indexes of the obs in
>> each cell
>> Or, viceversa, a vector of length n which tells, observation by
>> observation, which cell (out of the 3125) the observation is in.
>> stefano
>>
>> ______________________________________________
>> R-devel@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>
> --
> Brian D. Ripley, ripley@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
>



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https://stat.ethz.ch/mailman/listinfo/r-devel Received on Thu Feb 02 05:42:08 2006

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