[R] Better way to find distances between points in a set?

Carl Witthoft carl at witthoft.com
Wed Dec 10 00:49:24 CET 2008

I was playing around a bit to see how I could find the two points in a 
set of points (or ordered pairs)  furthest from each other.

Here's what I did:
1) created a Nrow by 2col matrix, so each row contains an x,y coordinate 

2) fed the matrix to a nested mapply (cv is my matrix):

mapply(function(k,l) mapply(function(x,y,a,b)
+ sqrt((x-a)^2+(y-b)^2),cv[,1],cv[,2],k,l),cv[,1],cv[,2])->alldist

Then I just did which.max(alldist) and found the original two points by 
figuring out what row, col the results of which.max referred to.

So, what's a better, or cleaner way to do all this?  That is, is there a 
function in some package that will do anything like my nested mapply 
thing, and is there a better tool than which.max for locating a position 
in a matrix?


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