[R] Spatial join between two datasets using x and y co-ordinates

[Steven McKinney]

> 
> -----Original Message-----
> From: r-help-bounces at r-project.org on behalf of Yasir Kaheil
> Sent: Tue 5/6/2008 4:24 PM
> To: r-help at r-project.org
> Subject: Re: [R] Spatial join between two datasets using x and y co-ordinates
>  
> 
> vector dat1.select is the selected records from dat1 by dat2.
> 
> > dat1.select<- dat1$x1 %in% dat2$x2 & dat1$y1 %in% dat2$y2
> > dat1[dat1.select,]
>        x1      y1 descript
> 1 1824615 5980732      cat
> 2 1823650 5983220      dog
> 

This won't always work, for example if another observation in dat1 had
the x coordinate of one of the dat2 entries and the y coordinate of
another:

> x1<-c(1824615,1823650,1821910,1823650)
> y1<-c(5980732,5983220,5990931,5980732)
> descript<-c("cat", "dog", "horse", "cow")
> dat1<-data.frame(x1,y1,descript)
> 
> x2<-c(1824615,1823650)
> y2<-c(5980732,5983220)
> dat2<-data.frame(x2,y2)
> 
> dat1
       x1      y1 descript
1 1824615 5980732      cat
2 1823650 5983220      dog
3 1821910 5990931    horse
4 1823650 5980732      cow
> dat2
       x2      y2
1 1824615 5980732
2 1823650 5983220
> 
> dat1.select<- dat1$x1 %in% dat2$x2 & dat1$y1 %in% dat2$y2
> dat1[dat1.select,]
       x1      y1 descript
1 1824615 5980732      cat
2 1823650 5983220      dog
4 1823650 5980732      cow
> 

merge() uses the key variables pasted together, to form a unique key,
e.g.

> dat1[match(paste(dat1$x1, dat1$y1, sep = "\r"), paste(dat2$x2, dat2$y2, sep = "\r"), nomatch = 0),]
       x1      y1 descript
1 1824615 5980732      cat
2 1823650 5983220      dog

see e.g. merge.data.frame



Steven McKinney

Statistician
Molecular Oncology and Breast Cancer Program
British Columbia Cancer Research Centre

email: smckinney +at+ bccrc +dot+ ca

tel: 604-675-8000 x7561

BCCRC
Molecular Oncology
675 West 10th Ave, Floor 4
Vancouver B.C. 
V5Z 1L3
Canada


> 
> 
> Andrew McFadden wrote:
> > 
> > Hi R users
> > 
> > I am trying to create a spatial join between two datasets. 
> > 
> > The first data set is large and contains descriptive data including x
> > and y co-ordinates. 
> > 
> > The second dataset is small and has been selected spatially. The only
> > data contained within the second dataset is the x and y coordinates only
> > i.e. no descriptive data.
> > 
> > The aim of a join made between the two datasets is to select those
> > points (and hence all the descriptive data) from dataset one that has
> > the same x and y co-ordinates as dataset two.
> > 
> > x1<-c(1824615,1823650,1821910)
> > y1<-c(5980732,5983220,5990931)
> > descript<-c("cat", "dog", "horse")
> > dat1<-data.frame(x1,y1,descript)
> > 
> > x2<-c(1824615,1823650)
> > y2<-c(5980732,5983220)
> > dat2<-data.frame(x2,y2)
> > 
> > dat1
> > dat2
> > 
> > The aim of the join is to produce:
> > 
> >        x1      y1 descript
> > 1 1824615 5980732      cat
> > 2 1823650 5983220      dog
> > 
> > And therefore limit the data in dataset 1 to that which has the same x
> > and y co-ordinates as dataset 2. 
> > 
> > Any suggestions?
> > 
> > Regards
> > 
> > Andy
> > 
> > 
> > Andrew McFadden MVS BVSc
> > Incursion Investigator
> > Investigation & Diagnostic Centres - Wallaceville Biosecurity New 
> > Zealand Ministry of Agriculture and Forestry
> > 
> > Phone 04 894 5600 Fax 04 894 4973 Mobile 029 894 5611 Postal address: 
> > Investigation and Diagnostic Centre- Wallaceville Box 40742 Ward St 
> > Upper Hutt
> > 
> > 
> > 
> > 
> > 
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> 
> 
> -----
> Yasir H. Kaheil, Ph.D.
> Catchment Research Facility
> The University of Western Ontario 
> 
> -- 
> View this message in context: http://www.nabble.com/Spatial-join-between-two-datasets-using-x-and-y-co-ordinates-tp17093486p17093656.html
> Sent from the R help mailing list archive at Nabble.com.

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