[R] Overlay of two graphs of different axes

[Greg Snow]

The zoomplot or updateusr functions in the TeachingDemos package may help.

But be cautious, the thing that grabs the most attention is where 2 (or more) lines cross, when you plot multiple lines on different scales the crossing is meaningless, but that meaningless point is what draws the eyes.  Your best option may be to do several juxtaposed plots using layout or par(mfrow....

-- 
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 Uwe Dippel
> Sent: Sunday, September 12, 2010 11:54 PM
> To: r-help at r-project.org
> Subject: [R] Overlay of two graphs of different axes
> 
> Though I have read quite a bit, and tried quite a bit, I have yet to
> find a nice way to overlay 2 or more curves in the same plot, with
> different ranges.
> Here is simplified sample code to demonstrate the question:
> 
>  > plot(2*(seq(1,5)), type="l", axes=FALSE)
>  > curve(2*(seq(1,5)), type="b", add=TRUE)
> Error in curve(2 * (seq(1, 5)), type = "b", add = TRUE) :
>    'expr' must be a function or an expression containing 'x'
>  > axis(2)
>  > curve(x^2, 1, 5, type="b", add=TRUE)
>  > axis(4)
> 
> Firstly, as an aside, I am not clear why 'curve' has a different syntax
> compared to 'plot'. As a still beginner, I'd for one would be happy to
> add curves to a plot; curves of just different parameters. Though, I
> guess, there must be a good reason?
> 
> Mostly, however, I wonder how to plot a number of curves into an
> original plot, that re-defines the min/max from the most recent curve.
> 
> In the example that I constructed, axis(2) does exactly the expected
> thing.
> What I want to do next, though, with the least effort, is to add
> another
> function in a manner that the added function is scaled, not according
> to
> the first function (plot), but to fit into the plotting area. (The
> example above overshoots the range).
> Plus, how can I subsequently add the axis suitable to the most recent
> function? That is, how can I render axis(4) to displaying the scale for
> the second graph, created with 'curve'?
> 
> Thanks in advance,
> 
> Uwe
> 
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