From: Gabor Grothendieck <ggrothendieck_at_gmail.com>

Date: Fri, 8 Feb 2008 23:46:56 -0500

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. Received on Sat 09 Feb 2008 - 04:50:17 GMT

Date: Fri, 8 Feb 2008 23:46:56 -0500

Try using dist:

ix <- 1:nrow(df.1)

m <- as.matrix(dist(rbind(df.1, df.2)))[ix, -ix]
which(min(m) == m, arr = TRUE)

On Feb 8, 2008 11:01 PM, Milton Cezar Ribeiro <milton_ruser_at_yahoo.com.br> wrote:

> Hi R-experts.

*>
**> I am working in a R-code where I have two datasets with x and y coordinates on each dataset.
**> I intent to identify the shortest distance between this two datasets. I wrote a short code to do that.
**> But when I join the datasets to compute the distances, the merge function run so slowly.
**> I need only to identify the index of rows from each dataset related to the shortest distance.
**>
**> x0<-rnorm(n=500,mean=1,sd=runif(1))
**> y0<-rnorm(n=500,mean=3,sd=runif(1))
**> x1<-rnorm(n=700,mean=8,sd=runif(1))
**> y1<-rnorm(n=700,mean=5,sd=runif(1))
**> df.0<-cbind(x0,y0)
**> df.1<-cbind(x1,y1)
**> plot(df.0,xlim=range(c(x0,x1)),ylim=range(c(y0,y1)))
**> points(df.1,col=2)
**> rm(x0,x1,y0,y1)
**>
**> #merge two data.frames of points
**> #### IT SPEND many time
**> df.merge<-merge(df.0,df.1,all=T)
**> #compute distances between each pair of points
**> attach(df.merge)
**> df.merge$distance<-((x0-x1)^2+(y0-y1)^2)^0.5
**> detach(df.merge)
**> #identify the minimum distance
**> df.merge.distance.min<-min(df.merge$distance)
**> #select the pair of points (x0,y0,x1,y1) with shortest distance
**> df.merge.distance.min.subset<-subset(df.merge,df.merge$distance<=df.merge.distance.min)
**> #trace a arrow between the points with shortest distance
**> arrows(df.merge.distance.min.subset[1,1],df.merge.distance.min.subset[1,2],df.merge.distance.min.subset[1,3],df.merge.distance.min.subset[1,4],code=0,col=3,lwd=2,lty=1)
**>
**> Any help are welcome
**>
**> Miltinho
**> Brazil.
**>
**>
**>
**> para armazenamento!
**>
**> [[alternative HTML version deleted]]
**>
**> ______________________________________________
**> 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.
**>
*

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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. Received on Sat 09 Feb 2008 - 04:50:17 GMT

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