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

Prof Brian Ripley ripley at stats.ox.ac.uk
Wed Jul 13 10:55:41 CEST 2005

```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)

On Wed, 13 Jul 2005, Robin Hankin wrote:

> Hi
>
> Ted makes a good point... matlab can dynamically rescale a plot in
> response
> to plot(...,add=TRUE) statements.
>
> 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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> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
>

--
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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