Hello,
R 4.0.2 on Ubuntu 20.04, sessionInfo at end.
This came up in r-help, I'm answering to the OP and also posting to
r-devel since I believe it is more appropriate there.
I can confirm this. The original instructions are the first and the
last, but even with smaller numbers the error shows up.
set.seed(2020)
jitter(c(1,2,10^4)) # desired behaviour
#[1] 1.058761 1.957690 10000.047401
jitter(c(0,1,10^4)) # bad behaviour
#[1] -92.43546 -1454.61126 8269.53754
jitter(c(-1,0,10^4)) # bad behaviour
#[1] -1484.3895 -427.5283 8010.3308
jitter(c(1,2,10^5)) # bad behaviour
#[1] 4809.238 10578.561 109753.430
To the OP: I am cc-ing this to r-devel@r-project.org.
Questions like this are about R itself and should be posted there.
sessionInfo()
R version 4.0.2 (2020-06-22)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 20.04.1 LTS
Matrix products: default
BLAS: /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.9.0
locale:
[1] LC_CTYPE=pt_PT.UTF-8 LC_NUMERIC=C
[3] LC_TIME=pt_PT.UTF-8 LC_COLLATE=pt_PT.UTF-8
[5] LC_MONETARY=pt_PT.UTF-8 LC_MESSAGES=pt_PT.UTF-8
[7] LC_PAPER=pt_PT.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=pt_PT.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] compiler_4.0.2
Hope this helps,
Rui Barradas
Às 11:32 de 23/09/20, Martin Keller-Ressel escreveu:
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 für Stochastische Analysis und Finanzmathematik
Technische Universität Dresden
Institut für Mathematische Stochastik
Willersbau B 316, Zellescher Weg 12-14
01062 Dresden
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