[R] Distances between two datasets of x and y co-ordinates

[Bill.Venables at csiro.au]

Here's what I would try.  Suppose x1, y1 and x2, y2 are the two data
sets.

z1 <- complex(real = x1, imaginary = y1)
z2 <- complex(real = x2, imaginary = y2)
dMat <- outer(z1, z2, function(z1, z2) Mod(z1-z2))

Bill Venables
CSIRO Laboratories
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mailto:Bill.Venables at csiro.au
http://www.cmis.csiro.au/bill.venables/ 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Andrew McFadden
Sent: Thursday, 13 March 2008 6:47 AM
To: r-help at r-project.org
Subject: [R] Distances between two datasets of x and y co-ordinates


Hi all

I am trying to determine the distances between  two datasets of x and y
points. The number of points in dataset One is very small i.e. perhaps
5-10. The number of points in dataset Two is likely to be very large
i.e. 20,000-30,000. My initial approach was to append the first dataset
to the second and then carry out the calculation:

dists <- as.matrix(dist(gis data from 2 * datasets)) 

However, the memory of the computer is not sufficient. A lot of
calculations carried out in this situation are unnecessary as I only
want approx 5 * 20,000 calculations versus 20,000 *20,000. 

x <- c(2660156,2663703,2658165,2659303,2661531,2660914)
y <- c(6476767,6475013,6475487,6479659,6477004,6476388)
data2<-cbind(x,y)

x <- c(266500,2611111)
y <- c(6478767,6485013)
data1<-cbind(x,y)

Any suggestions on how to do this would be appreciated.

Regards

Andrew

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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