jitter-bug? problematic behaviour of the jitter function
Dear all, i have noticed some strange behaviour in the ?jitter? function in R. On the help page for jitter it is stated that "The result, say r, is r <- x + runif(n, -a, a) where n <- length(x) and a is the amount argument (if specified).? and "If amount is NULL (default), we set a <- factor * d/5 where d is the smallest difference between adjacent unique (apart from fuzz) x values.? This works fine as long as there is no (very) large outlier
jitter(c(1,2,10^4)) # desired behaviour
[1] 1.083243 1.851571 9999.942716 But for very large outliers the added noise suddenly ?jumps? to a much larger scale:
jitter(c(1,2,10^5)) # bad behaviour
[1] -19535.649 9578.702 115693.854 # Noise should be of order (2-1)/5 = 0.2 but is of much larger order. This probably does not matter much when jitter is used for plotting, but it can cause problems when jitter is used to break ties. best regards, Martin -------------------------------- Martin Keller-Ressel Professor f?r Stochastische Analysis und Finanzmathematik Technische Universit?t Dresden Institut f?r Mathematische Stochastik Willersbau B 316, Zellescher Weg 12-14 01062 Dresden --------------------------------