base (version 3.3)

jitter: ‘Jitter’ (Add Noise) to Numbers

Description

Add a small amount of noise to a numeric vector.

Usage

jitter(x, factor = 1, amount = NULL)

Arguments

x

numeric vector to which jitter should be added.

factor

numeric.

amount

numeric; if positive, used as amount (see below), otherwise, if = 0 the default is factor * z/50.

Default (NULL): factor * d/5 where d is about the smallest difference between x values.

Value

jitter(x, ...) returns a numeric of the same length as x, but with an amount of noise added in order to break ties.

Details

The result, say r, is r <- x + runif(n, -a, a) where n <- length(x) and a is the amount argument (if specified).

Let z <- max(x) - min(x) (assuming the usual case). The amount a to be added is either provided as positive argument amount or otherwise computed from z, as follows:

If amount == 0, we set a <- factor * z/50 (same as S).

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.

References

Chambers, J. M., Cleveland, W. S., Kleiner, B. and Tukey, P.A. (1983) Graphical Methods for Data Analysis. Wadsworth; figures 2.8, 4.22, 5.4.

Chambers, J. M. and Hastie, T. J. (1992) Statistical Models in S. Wadsworth & Brooks/Cole.

See Also

rug which you may want to combine with jitter.

Examples

round(jitter(c(rep(1, 3), rep(1.2, 4), rep(3, 3))), 3)
## These two 'fail' with S-plus 3.x:
jitter(rep(0, 7))
jitter(rep(10000, 5))