[R] overlay plots
murdoch at stats.uwo.ca
Thu Sep 6 17:36:40 CEST 2001
On Thu, 06 Sep 2001 15:08:16 +0100, you wrote in message
<OF62D87A41.4733FB80-ON80256ABF.004D2E97 at cso.ie>:
>I new to R (I don't know anything about S+ either!)
>I've a simple question:
>How do I generate overlay plots in R?
>So far as I can see the plot(x, y) operator will only give me one graph and
>the plot(x ~ y + z) will give me 2 separate plots.
>Is there an easy way to overlay or am I missing the obvious?
>Any help welcome.
The general scheme in R (and S+) is that one call sets up a plotting
region and establishes a coordinate system, and possibly fills it, and
then further calls can be used to embellish it.
What you want to do is to use one call to plot y vs. x, then add the z
vs. x points to that plot. A simple way to do that is
Note that the horizontal coordinate is listed first when you list
arguments, but the vertical coordinate is listed first when you use a
formula, so this is equivalent:
plot(y ~ x)
points(z ~ x)
Because the first call establishes the coordinates, you might find
that not all the z values are shown. To guarantee this, you can use
optional arguments in the first call, e.g.
plot(x, y, ylim = range(c(y,z)))
You should also look at "axis", "lines", "text", "mtext", "box" etc.
for other functions to embellish the plot.
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