[R] pretty not pretty
Martin Maechler
maechler at stat.math.ethz.ch
Wed Oct 30 11:56:36 CET 2002
>>>>> "DavidB" == David Brahm <brahm at alum.mit.edu>
>>>>> on Tue, 29 Oct 2002 10:31:17 -0500 writes:
DavidB> Ott Toomet <otoomet at econ.au.dk> wrote:
>> Pretty (R 1.5.1) has problems with zero:
>> pretty(smallch)
DavidB> [1] -2.00000e-02 -3.469447e-18 2.00000e-02 4.00000e-02 6.00000e-02
DavidB> [6] 8.000000e-02 1.000000e-01 1.200000e-01
>> You notice -3.46e-18 instead of 0. Is this feature changed in 1.6.0,
>> or are there any simple ways to get around of it?
DavidB> I mentioned this in R-devel on June 14, 2002
DavidB> ("pretty() sometimes isn't"). It derives from the
DavidB> roundoff error introduced in seq(-.02, .12,
DavidB> length=8). I suggested that the last line of the
DavidB> code for pretty() should get a zapsmall() around it:
DavidB> pretty <- function(...) {
DavidB> ...
DavidB> zapsmall(seq(z$l, z$u, length = z$n + 1))
DavidB> }
DavidB> Since that hasn't been implemented, you could simply
DavidB> put a zapsmall() around every pretty() in your code.
It *) now _has_ been implemented. ---> will be in R-beta tomorrow
and R 1.6.1.
Whereas for seq() it is clear that you will see these roundoffs,
they are ``wrong'' for pretty().
Thank you David, for the reminder.
*) I've used zapsmall(seq(z$l, z$u, length = z$n + 1), digits = 7)
instead in order to make sure that the result will not depend
on options("digits").
Martin Maechler <maechler at stat.math.ethz.ch> http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum LEO C16 Leonhardstr. 27
ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND
phone: x-41-1-632-3408 fax: ...-1228 <><
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