[R] Minimum distance

[Mulholland, Tom]

Since it is not clear exactly what you require, I have assumed that what you are looking for is the minimum value for each row or column depending upon which is airports and which is the towers.

Is this what you are looking for

x <- runif(100)
dim(x) <- c(5,20)
apply(x,1,function(y) which(y == min(y)))

The only issue I see here is that there may be more than one minimim in which case the value returned will be a list with all of the matched values which would need to be processed

 x <- trunc(runif(100) * 10)
 dim(x) <- c(5,20)
 apply(x,1,function(y) which(y == min(y)))
 
If you did not have a method for processing you could order the towers in some preferred order and just take the first match

apply(x,1,function(y) head(which(y == min(y)),1))

If you are talking about a matrix where you need to find the shortest path, you might want to look at the package e1071. I think the function is called allShortestPaths

Tom

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch]On Behalf Of 
> Williams, Michael
> Sent: Monday, 18 April 2005 7:58 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Minimum distance
> 
> 
> G'day, I have a matrix 20000 x 500 populated with all the distances
> between a list of airports and a list of towers. What I'm 
> having trouble
> doing is finding the closest airport to each tower, Any help would be
> greatly appreciated.
> 
> Regards,
> Michael Williams
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
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