Other useful R functions blogs and pages

Paul Johnson's R Page

Li Chen's R page

James Forester R Functions' Blog 

R blog

calculating angle from xy coordinates

## from north (-pi,pi) positive toward east
angle.north = function(xx,yy){sign(xx)*(yy<0)*pi + atan(xx/yy)}

## from east (0,2.pi) positive toward north
angle = function(xx,yy){atan(yy/xx) - sign(xx)*sign(yy)*pi*(xx<0)}

empirical distributions CDF

"empirical CDF's are not good at showing differences in the tails of a distribution"
Owen, A. B., Empirical Likelihood, 2001, Chapman & Hall/CRC, pg 10.