# [R] How to use the function "plot" as Matlab

(Ted Harding) Ted.Harding at nessie.mcc.ac.uk
Wed Jul 13 12:01:42 CEST 2005

```On 13-Jul-05 Prof Brian Ripley wrote:
> For most purposes it is easiest to use matplot() to plot superimposed
> plots like this.  E.g.
>
> x <- 0.1*(0:20)
> matplot(x, cbind(sin(x), cos(x)), "pl", pch=1)

This, and Robin's suggestion, are good practical solutions especially
when only a few graphs (2 or 3 or ... ) are involved. However, their
undelying principle is to accumulate auxiliary variables encapsulating
the graphs which will eventually be plotted.

However, once in a while I like to make a really messy graph of
superimposed sample paths of a simulated stochastic process, perhaps
with several dozen replications and many points (even 5000) along
each sample path. An example where this has a real practical point
is diffusion from the chimney stack of, say, an incinerator. The
resulting plot can give a good picture of the "average plume",
allowing the viewer to form an impression of the variation in
concentration along and on the fringes of the plume.

This is definitely a case where "dynamic rescaling" could save
hassle! Brian Ripley's suggestion involves first building a
matrix whose columns are the replications and rows the time-points,
and Robin Hankin's could be easily adapted to do the same,
though I think would involve a loop over columns and some very
long vectors.

How much easier it would be with dynamic scaling!

Best wishes,
Ted.

> On Wed, 13 Jul 2005, Robin Hankin wrote:
>
>> Hi
>>
>> Ted makes a good point... matlab can dynamically rescale a plot in
>> response
>>
>> For some reason which I do not understand, the rescaling issue is
>> only a problem
>> for me when working in "matlab mode".  It's not an issue when working
>> in "R mode"
>>
>> Ted pointed out that the following does not behave as intended:
>>
>>
>>>   x = 0.1*(0:20);
>>>   plot(x,sin(x))
>>>   lines(x,1.5*cos(x))
>>
>>
>> and presented an alternative method in which ylim was set by hand.  I
>> would suggest:
>>
>> x <- 0.1*(0:20)
>> y1 <- sin(x)
>> y2 <- 1.5*cos(x)
>>
>> plot(c(x,x),c(y1,y2),type="n")
>> lines(x,y1)
>> lines(x,y2)
>>
>> because this way, the axes are set by the plot() statement, but
>> nothing is plotted.
>>
>>
>> best wishes
>>
>> rksh
>>
>>
>>
>>
>>
>> On 13 Jul 2005, at 09:12, (Ted Harding) wrote:
>>>>
>>>
>>> Although this is an over-worked query -- for which an answer, given
>>> that t="l" has been specified, is to use
>>>
>>>   plot(a,t="l",col="blue",ylim=c(0,10))
>>>   lines(b,t="l",col="red")
>>>
>>> there is a more interesting issue associated with it (given that
>>> Klebyn has come to it from a Matlab perspective).
>>>
>>> It's a long time since I used real Matlab, but I'll illustrate
>>> with octave which, in this respect, should be identical to Matlab.
>>>
>>> Octave:
>>>
>>> octave:1> x = 0.1*(0:20);
>>> octave:2> plot(x,sin(x))
>>>
>>> produces a graph of sin(x) with the y-axis scaled from 0 to 1.0
>>> Next:
>>>
>>> octave:3> hold on
>>> octave:4> plot(x,1.5*cos(x))
>>>
>>> superimposes a graph of 1.5*cos(x) with the y-axis automatically
>>> re-scaled from -1 to 1.5.
>>>
>>> This would not have happened in R with
>>>
>>>   x = 0.1*(0:20);
>>>   plot(x,sin(x))
>>>   lines(x,1.5*cos(x))
>>>
>>> where the 0 to 1.0 scaling of the first plot would be kept for
>>> the second, in which therefore part of the additional graph of
>>> 1.5*cos(x) would be "outside the box".
>>>
>>> No doubt like many others, I've been caught on the wrong foot
>>> by this more than a few times. The solution, of course (as
>>> illustrated in the reply to Klebyn above) is to anticipate
>>> what scaling you will need for all the graphs you intend to
>>> put on the same plot, and set up the scalings at the time
>>> of the first one using the options "xlim" and "ylim", e.g.:
>>>
>>>   x = 0.1*(0:20);
>>>   plot(x,sin(x),ylim=c(-1,1.5))
>>>   lines(x,1.5*cos(x))
>>>
>>> This is not always feasible, and indeed should not be expected
>>> to be feasible since part of the reason for using software
>>> like R in the first place is to compute what you do not know!
>>>
>>> Indeed, R will not allow you to use "xlim" or "ylim" once the
>>> first plot has been drawn.
>>>
>>> So in such cases I end up making a note (either on paper or,
>>> when I do really serious planning, in auxiliary variables)
>>> of the min's and max's for each graph, and then re-run the
>>> plotting commands with appropriate "xlim" and "ylim" scaling
>>> set up in the first plot so as to include all the subsequent
>>> graphs in entirety. (Even this strategy can be defeated if
>>> the succesive graphs represent simulations of long-tailed
>>> distributions. Unless of course I'm sufficiently alert to
>>> set the RNG seed first as well ... )
>>>
>>> I'm not sufficiently acquainted with the internals of "plot"
>>> and friends to anticipate the answer to this question; but,
>>> anyway, the question is:
>>>
>>>   Is it feasible to include, as a parameter to "plot", "lines"
>>>   and "points",
>>>
>>>     rescale=FALSE
>>>
>>>   where this default value would maintain the existing behaviour
>>>   of these functions, while setting
>>>
>>>     rescale=TRUE
>>>
>>>   would allow each succeeding plot, adding graphs using "points"
>>>   or "lines", to be rescaled (as in Matlab/Octave) so as to
>>>   include the entirety of each successive graph?
>>>
>>> Best wishes to all,
>>> Ted.
>>>
>>>
>>> --------------------------------------------------------------------
>>> E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
>>> Fax-to-email: +44 (0)870 094 0861
>>> Date: 13-Jul-05                                       Time: 09:12:34
>>> ------------------------------ XFMail ------------------------------
>>>
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>>
>> --
>> Robin Hankin
>> Uncertainty Analyst
>> National Oceanography Centre, Southampton
>> European Way, Southampton SO14 3ZH, UK
>>  tel  023-8059-7743
>>
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>>
>
> --
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>
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