[R] Pointing to a specific place on the x-axis with an arrow

[Barry Rowlingson]

On Wed, Oct 6, 2010 at 1:45 AM, Josh B <joshb41 at yahoo.com> wrote:
> Hi all,
>
> I am trying to do something simple, but which is deviling me. I want to add an
> up-arrow to the x-axis, pointing to a specific location on the axis. I want the
> arrow to be as large as possible.
>
> Here is where I'm at with my code:
>
> #this part if from the ?plot example:
> require(stats)
> plot(cars)
> lines(lowess(cars))
> #I am trying to use mtext to add the arrow... but I don't know how to do it:
> mtext("?", side = 1, line = 0, at = 7)
> #that question mark is a place-holder for the arrow. How do I put an up-arrow
> there instead of the question mark -- as large as possible?

 Use %up% in an expression - but I think it needs two empty {}
expressions as arguments:

mtext(expression({}%up%{}), side = 1, line = 0, at = 12)

Looks pretty good...

Barry

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