jitter
‘Jitter’ (Add Noise) to Numbers
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 isfactor * z/50
.Default (
NULL
):factor * d/5
whered
is about the smallest difference betweenx
values.
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.
Value

jitter(x, ...) returns a numeric of the same length as
x, but with an amount of noise added in order to break
ties.
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
library(base)
round(jitter(c(rep(1, 3), rep(1.2, 4), rep(3, 3))), 3)
## These two 'fail' with Splus 3.x:
jitter(rep(0, 7))
jitter(rep(10000, 5))