[Moved to R-devel, where it probably should have started and it is
getting to C-level functions now.]
abline is not 'misbehaving' (don't be rude about the work of
volunteers who are in your audience), but behaving in the same way as
other graphics calls.
The real story is this (and R is Open Source, so you can read the code
too).
Most base graphics functions call GClip to set the graphics clip state
before drawing). GClip only does anything if the xpd state has
changed since the last time it was used, and in the case of a plot
like this with axes which were drawn in the margins, it has done so.
Now, the tricky bit is 'was used', which can be very hard to
determine. Just setting the par is not enough: it has to be 'used'.
What I have done in R-devel is make clip() 'use' xpd, and that will
ensure that the clip region it sets persists until xpd is next
changed. There the example works as I believe you intended.
On Sat, 24 Jan 2009, Greg Snow wrote:
This is a known issue, the documentation of clip talks about some plotting
functions resetting the clipping region and some don't. abline is apparently
one of those that plots first, then resets the clipping region (so the first
time it doesn't acknowledge it, but does afterwards). The function clipplot in
the TeachingDemos package uses a similar kludge to what you do below (and I
guess that puts my standing in the hall of fame at even higher risk than yours)
except that it uses the box function with a transparent box to reset the
clipping region, which means that you get strange boxes if your graphics device
does not handle transparency. It was a question like yours that I asked in
order to try to eliminate the kludge from clipplot that originally lead to the
clip function being added, and it does cover the initial cases that I asked
about.
In order to change things to work like we would like (always resetting the
clipping region at the appropriate place so that clip always does what we
expect) will probably require going through every basic command that could put
something into the plot and figure out exactly when to have them reset the
clipping region (which may not be a simple decision, doing it too early may
break existing code). The amount of tedious work required for not much return
places this fairly low on the priority list, especially when there is a work
around (as you have found), even if it feels like a bit of a kludge.
So while this probably does not fix your problem, at least hopefully this helps
you understand a bit more of what is happening here, and at least you know that
you are not alone in hall of kludge infamy.
--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.s...@imail.org
801.408.8111
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-
project.org] On Behalf Of Jim Lemon
Sent: Saturday, January 24, 2009 2:51 AM
To: r-h...@r-project.org
Subject: [R] Is abline misbehaving?
Hi experts,
I was graciously offered a function to enhance abline by restricting
the
extent of the line to less than the plotting region. This seems a
useful
idea, and it looked like the easiest way to program it was to set up a
clipping region with "clip", draw the abline and then restore the
previous clipping region. Let us call this function ablineclip. After
quite a bit of testing, I have found that the first call to ablineclip
ignores the clipping region. It's not that simple. Successive calls to
ablineclip respect the clipping region, even if it changes. I can
reproduce the behavior like this:
plot(-3:3,-3:3)
clip(-2,2,-2,2)
abline(v=0)
clip(-2,2,-2,2)
abline(h=0)
The first abline ignores the clip, the second respects it. I have
programmed around this, with the pathetic kludge of calling "abline"
with a line outside the plotting area, calling "clip" a second time,
and
then calling "abline" with the line that was requested. While this
works, my place in programming history will be ineradicably compromised
if the Programmers' Hall of Fame ever finds out. Any suggestions?
R-2.7.2
FC9 Linux
Jim
______________________________________________
r-h...@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-
guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
r-h...@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
