[R] grid.edit problem

[Gabor Grothendieck]

Thanks, again.  I see its basically an origin problem so that, for
example, this would have worked too:

grid.edit("L", x = grid.get("L")$x + unit(10, "native") - unit(0, "native"))

By the way, could unit.c, unit.rep and unit.length
be named c.unit, rep.unit and length.unit (since
then they would just be methods of the respective
S3 generics and no new names would need to be
introduced or remembered).


On 10/16/05, Paul Murrell <p.murrell at auckland.ac.nz> wrote:
> Hi
>
>
> Gabor Grothendieck wrote:
> > I am having a problem in editing a grob.  It works ok if I try to
> > shift the grob using npc coordinates but if I do the same thing
> > using native coordinates the grob disappears.  What is wrong?
> >
> >
> > library(grid)
> > grid.newpage()
> >
> > # create viewport
> > pushViewport(viewport(xscale = c(100,200), name = "X"))
> >
> > # draw vertical line
> > grid.lines(150, 0:1, default.units = "native",  name = "L")
> >
> > # move line 25% of the way to the right. Works ok.
> > grid.edit("L", x = grid.get("L")$x + unit(0.25, "npc"))
> >
> >
> > # but now repeat it shifting it using native coordinates
> > ########################################################
> >
> > # remove line and draw a new line where the original one was
> > grid.remove("L")
> > grid.lines(150, 0:1, default.units = "native",  name = "L")
> >
> > # move line 25% of the way to the right but use native coordiantes
> > #### line disappears !!!!!!!!!
> > grid.edit("L", x = grid.get("L")$x + unit(25, "native"))
>
>
> This is due to the fact that the *location* unit(25, "native") is very
> different from the *location* unit(.25, "npc").   In your example, the
> former actually corresponds to unit(-.75, "npc").
>
> What you appear to be trying to do is add a *dimension* (width) unit(25,
> "native"), which corresponds to a *dimension* unit(.25, "npc"), to the
> original *location* unit(150, "native").  Problem is, the 'x' component
> of a  "line" is interpreted as a location so your unit(25, "native") is
> interpreted as a location.
>
> This issue is described in one of the small grid doc's at
> http://www.stat.auckland.ac.nz/~paul/grid/doc/locndimn.pdf
>
> A (rather verbose) way of specifying your goal is the following ...
>
> grid.edit("L", x = grid.get("L")$x +
>                    # Convert a width into a location
>                    convertUnit(unit(25, "native"), "native",
>                                "x", "dimension", "x", "location"))
>
> ... or, if you know you are only dealing with "native" (data) values,
> you could add them together before using them to specify a location ...
>
> x <- 150 + 25
> grid.edit("L", x = unit(x, "native"))
>
> Paul
> --
> Dr Paul Murrell
> Department of Statistics
> The University of Auckland
> Private Bag 92019
> Auckland
> New Zealand
> 64 9 3737599 x85392
> paul at stat.auckland.ac.nz
> http://www.stat.auckland.ac.nz/~paul/
>
>