[Rd] [R] Is abline misbehaving?

[Greg Snow]

Apparently the fix was simpler than I anticipated (at least for Prof. Ripley).

Thanks for finding and implementing this improvement.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: Prof Brian Ripley [mailto:ripley at stats.ox.ac.uk]
> Sent: Thursday, February 05, 2009 6:42 AM
> To: Greg Snow
> Cc: Jim Lemon; r-devel at r-project.org
> Subject: Re: [R] Is abline misbehaving?
> 
> [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.snow at imail.org
> > 801.408.8111
> >
> >
> >> -----Original Message-----
> >> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> >> project.org] On Behalf Of Jim Lemon
> >> Sent: Saturday, January 24, 2009 2:51 AM
> >> To: r-help at 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-help at 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-help at 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,                  ripley at 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