[R] Pointer to covariates?

[Anne York]

Here is another idea, but the overhead might be just as great.

dat_data.frame(y=1:3,x1=c(1,0,1),x2=c(0,1,0))
dat.unique_unique(paste(as.character(dat$x1),as.character(dat$x2)))
dat.keys_match(paste(as.character(dat$x1),as.character(dat$x2)),dat.unique)


> > dat
  y x1 x2
1 1  1  0
2 2  0  1
3 3  1  0
> dat.unique
[1] "1 0" "0 1"
> dat.keys
[1] 1 2 1
> 


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Anne E. York
National Marine Mammal Laboratory
Seattle WA 98115-0070  USA
e-mail: anne.york at noaa.gov
Voice: +1 206-526-4039
Fax: +1 206-526-6615
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On Thu, 21 Feb 2002, [iso-8859-1] Göran Broström wrote:

>On Wed, 20 Feb 2002, Gabor Grothendieck wrote:
>
>> In the first line, use the dist function, found in library mva,
>> to get the distance between each pair of rows.   From this
>> calculate an incidence matrix for which element i,j is true if 
>> row i in dat equals row j in dat (and false elsewhere).
>> 
>> In the second line, for each row calculate the indices of 
>> the matching rows and take the minimum of those as the key.
>> 
>> incid <- as.matrix(dist(dat[,-1],method="max"))==0
>> keys <- unlist(lapply(apply(incid,1,which),min))
>
>Thank you very much! This is very fast, much faster than my attempts
>so far, but it has two drawbacks:
>
>1. It  gives pointers to first occurrences in the _original_ data frame,
>not the 'unique' version.
>
>2. The first step results in a _huge_ matrix 'incid', too huge for my 
>applications.
>
>However, this is a promising first attempt, and I will try to refine
>the idea. Again, thanks!
>
>Göran
>
>> 
>> --- Göran Broström <gb at stat.umu.se> wrote:
>> >I have a dataframe 'dat' with one response and some covariates. Many 
>> >observations  (rows), but only a few unique combinations of 
>> >the covariates. Let's say that the response is in column 1, and 
>> >the covariates in columns 2:k.
>> >
>> >I want to do 
>> >
>> >> covar <- unique.data.frame(dat[, 2:k])
>> >> y <- dat[, 1]
>> >> keys <- ??????
>> >
>> >where 'keys' should be a vector of length length(y) and contain the
>> >row numbers in 'covar', where the response will find its covariates.
>> >
>> >Example:
>> >
>> >> dat
>> >  y x1 x2
>> >1 1  1  0
>> >2 2  0  1
>> >3 3  1  0
>> >
>> >> unique.data.frame(dat[, 2:3])
>> >  x1 x2
>> >1  1  0
>> >2  0  1
>> >
>> >> keys
>> >1  1
>> >2  2
>> >3  1
>> >
>> >But how do I get 'keys'?
>> >-- 
>> > Göran Broström                      tel: +46 90 786 5223
>> > professor                           fax: +46 90 786 6614
>> > Department of Statistics            http://www.stat.umu.se/egna/gb/
>> > Umeå University
>> > SE-90187 Umeå, Sweden             e-mail: gb at stat.umu.se
>> >
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>
>-- 
> Göran Broström                      tel: +46 90 786 5223
> professor                           fax: +46 90 786 6614
> Department of Statistics            http://www.stat.umu.se/egna/gb/
> Umeå University
> SE-90187 Umeå, Sweden             e-mail: gb at stat.umu.se
>
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>

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