[R] overlay plots
maechler at stat.math.ethz.ch
Fri Sep 7 09:02:51 CEST 2001
>>>>> "Duncan" == Duncan Murdoch <murdoch at stats.uwo.ca> writes:
Duncan> On Thu, 06 Sep 2001 15:08:16 +0100, you wrote in message
Duncan> <OF62D87A41.4733FB80-ON80256ABF.004D2E97 at cso.ie>:
>> Hi all!
>> 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.
Duncan> The general scheme in R (and S+) is that one call sets up a
Duncan> plotting region and establishes a coordinate system, and
Duncan> possibly fills it, and then further calls can be used to
Duncan> embellish it.
Duncan> What you want to do is to use one call to plot y vs. x, then
Duncan> add the z vs. x points to that plot. A simple way to do that
Duncan> plot(x, y)
Duncan> points(x, z)
Duncan> Note that the horizontal coordinate is listed first when you
Duncan> list arguments, but the vertical coordinate is listed first
Duncan> when you use a formula, so this is equivalent:
Duncan> plot(y ~ x)
Duncan> points(z ~ x)
Duncan> Because the first call establishes the coordinates, you might
Duncan> find that not all the z values are shown. To guarantee this,
Duncan> you can use optional arguments in the first call, e.g.
Duncan> plot(x, y, ylim = range(c(y,z)))
Duncan> You should also look at "axis", "lines", "text", "mtext", "box" etc.
Duncan> for other functions to embellish the plot.
But if it's really as simple, you might also think of using
matplot(), matlines(),... which are useful wrappers to
one plot(.) + several points() / lines() calls. For the above example,
Martin Maechler <maechler at stat.math.ethz.ch>
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