[R] position legend below x-axis title

Greg Snow Greg.Snow at imail.org
Thu Jul 3 18:00:18 CEST 2008

Look at ?grconvertY, you can use this to convert from 'ndc' (normalized device coordinates) where 0 is the bottom of the device (window/page/...) to user coordinates that can be used in legend or other functions.

Hope this helps,

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 Anne-Marie Ternes
> Sent: Wednesday, July 02, 2008 3:42 AM
> To: r-help at r-project.org
> Subject: [R] position legend below x-axis title
> Dear helpers,
> I'm using a R script on several different datasets, which
> makes that axis scales may vary quite a lot from dataset to
> dataset. So what I'm looking for now, is how to automagically
> find out how to position the legend (horizontal) in the space
> below the x-axis title, and how to make sure that the legend
> is within the limits of the lower inner or outer margin?
> I'm aware of plot, device and figure regions, and of the
> "din, fin, pin, usr, mai, mar, omi, oma and xpd" parameters,
> of inner and outer margins.
> I cannot simply position my legend on "minus something", as
> that depends on "usr" coordinates, and those depend on the
> scale of the y-axis.
> I tried finding the ideal spot by taking the figure height
> and subtracting the upper margin, the height of the plot
> region, and half of the lower margin. This is quite tedious
> and doesn't help me, as I get a spot in inches, which doesn't
> to correspond to the "usr"
> coordinates.
> I also tried to convert between inches and "usr" coordinates
> using "xy.coords", but the result did not correspond to the
> position returned by "locator".
> I'm also aware of "mtext" and its fabulous arguments "side"
> and "line", but there I loose the functionality of displaying
> the legend symbols.
> Finally, I found a hint about using "layout", but there I
> admit I would need more than a hint - a small tutorial or
> graphical example with code would be very helpful.
> So, the question is, if there is per chance a way to pass
> "side" and "line" arguments to "legend", and if not, what is
> the best way to do what I try to do? BTW, the plot types
> involved are mostly line plots and barplots.
> Thanks a lot for your help,
> Anne-Marie
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