R help - Nov 2005 - absolute position in plot()

dear R wizards:  could you please point me into the right direction?  I
would like to write a general function arrow(x1,y1,x2,y2), which
naturally draws an arrow.

the basics of writing this function are of course easy.  the only
complication is that I would like the arrow not to exactly hit (x2,y2),
but to stop short just a "tiny bit."  alas, because I want my arrow()
function to be general, I would rather not have to tell it the xlim and
ylim plot parameters.  So, I need something more akin to the absolute
positioning by which the argument "pos" works within the text()
function.  In fact, optimally, I would adopt the default distance that
the "pos=x" uses, and have an optional parameter that allows the user
to
change this.

could someone please point me to an example of how to do something like
this?

regards,

/iaw

See getcell at:

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/63579.html

which converts between absolute and user coordinates.  It
should give you insight to allow you to develop this functionality.

On 11/11/05, ivo welch <ivo_welch at mailblocks.com>
wrote:
>
> dear R wizards:  could you please point me into the right direction?  I
> would like to write a general function arrow(x1,y1,x2,y2), which
> naturally draws an arrow.
>
> the basics of writing this function are of course easy.  the only
> complication is that I would like the arrow not to exactly hit (x2,y2),
> but to stop short just a "tiny bit."  alas, because I want my
arrow()
> function to be general, I would rather not have to tell it the xlim and
> ylim plot parameters.  So, I need something more akin to the absolute
> positioning by which the argument "pos" works within the text()
> function.  In fact, optimally, I would adopt the default distance that
> the "pos=x" uses, and have an optional parameter that allows the
user to
> change this.
>
> could someone please point me to an example of how to do something like
> this?
>
> regards,
>
> /iaw
>
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