[R] Prevent sequential repeated values in data frame column

[Scott Sherrill-Mix]

It's a pretty inefficient way to do things (e.g. 50000+ iterations [20
seconds] to find a good sample) but if you're not doing this often I
guess you could do something like:

checkNeighborEqual<-function(x){
 #assuming the final value is not infinity
 return(any(x==c(x[-1],Inf)))
}

#fake data
x<-data.frame('distance'=rep(1:10,3),'angle'=rep(1:5,6),'var3'=rep(1:6,5))

#column that should not have adjacent duplicates
noDupeColumns<-c('angle','var3')
run<-1
while(run==1||any(apply(newX[,noDupeColumns],2,checkNeighborEqual))){
 message('Scrambling for the ',run,' time')
 newX<-x[sample(1:nrow(x),nrow(x)),]
 run<-run+1
}
print(newX)

Scott



Scott Sherrill-Mix
Department of Microbiology
University of Pennsylvania
402B Johnson Pavilion
3610 Hamilton Walk
Philadelphia, PA  19104-6076


On Tue, Aug 11, 2009 at 4:25 PM, Jon Zadra<jrz9f at virginia.edu> wrote:
> Hi,
>
> I'm trying to randomize a sequence of trials for an experimental design.
>  The trials consist of values for each of two factors.  As is there are 30
> combinations of the two factors, and I want them to be ordered randomly but
> with the requirement that for one of the factors, the value can never be the
> same as the previous value.
>
> I'm currently randomizing my dataframe by using:
>
>  x[sample(1:nrow(x), nrow(x),]
>
> Output example, on rows 2 and 3 the angle value is the same (the situation I
> wish to prevent):
>   Distance Angle
>        9    90
>        9    45
>       10   45
>       11   30
>        8    60
>        7     0
>        8    30
>       10     0
>       10    60
>        ...    ...
>
> Can anyone recommend a simple way to do this?  (Bonus if it could be
> implemented for more than a single column!)
>
> Thanks in advance,
>
> Jon
> --
> Jon Zadra
> Department of Psychology
> University of Virginia
> P.O. Box 400400
> Charlottesville VA 22904
> (434) 982-4744
> email: zadra at virginia.edu
> <http://www.google.com/calendar/embed?src=jzadra%40gmail.com>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>