[R] r function for calculating extreme spread in group

[Ben Bolker]

Steven Matthew Anderson <adastra69 <at> mac.com> writes:

> I'm trying to figure out how to write a r function that will calculate  
> the extreme spread of a group of points given their (x,y)  
> coordinates.  Extreme Spread is the maximal Euclidean distance between  
> two points in a group
> 
> ex.spread = max{ sqrt [ (xi-xj)^2 - (yi-yj)^2 ] } for i not equal to j
> 
> I have 60 levels to apply this to.
> 

   how about something like

max(dist(cbind(x,y))   ... ???

(or to do this in a data frame d with columns x, y, and g (group),

sapply(split(d,d$g),function(Z)max(dist(Z[,c("x","y")])))

  Ben Bolker