[R] par("usr") trouble in multiplot axis scaling

[Johannes Graumann]

You were right! 'ylim' does what I want!
Thanks for deciphering my cryptic scribble and helping out!

Joh

On Mon, 25 Oct 2004 14:25:55 -0500
Marc Schwartz <MSchwartz at MedAnalytics.com> wrote:

> On Mon, 2004-10-25 at 13:19, Johannes Graumann wrote:
> > Hello,
> > 
> > I'm blotting a series of growth curves into a multiplot environment
> > created with layout().
> > since I want the four plots to be easily visually comparable, I do
> > the following:
> > 
> > #first plot
> > plot(x,y,<stuff>)
> > standarduser<-par()$usr
> > ...
> > <some fitting>
> > ...
> > lines(spline(x, <fitted_equation>))
> > 
> > #everything all right till here
> > # second plot
> > plot(x,y,<stuff>)
> > par(usr=standarduser)
> > ...
> > <some fitting>
> > ...
> > lines(spline(x, <fitted_equation>))
> > 
> > The problem here is, that the axis of the second plot seem to be
> > scaled according to the parameters of the first, BUT the fitted
> > curve in the second plot isn't!
> > 
> > Any idea about what I'm doing wrong?
> > 
> > Please help this newbie out of his misery!
> > 
> > Joh
> 
> If I am correctly understanding what you are doing and what you want,
> you would like each of the four plots to have the same axis ranges?
> 
> Part of the problem, I think, is that in your second plot(), the axis
> ranges are automatically set based upon the ranges of your x and y
> data in that call. These presumably are different than the x and y
> values in your first plot? 
> 
> Thus, the initial plot region scales are going to be different for
> each plot. By default, this will be range(x) +/- 4% and range(y) +/-
> 4%.
> 
> When you force the second plot region's values to be 'standarduser',
> your underlying x,y plot, having already been drawn, and the new lines
> to be added are then on different scales in the same plot.
> 
> If my assumptions are correct, you would be better off calling plot()
> each time using the 'xlim' and 'ylim' arguments to explicitly define
> the axis ranges with known common values.
> 
> For example, if you know that the range of all x values is r.x and the
> range of all y values is r.y:
> 
> #first plot
> plot(x, y, <stuff>, xlim = r.x, ylim = r.y)
> ...
> <some fitting>
> ...
> lines(spline(x, <fitted_equation>))
> 
> 
> # second plot
> plot(x, y, <stuff>, xlim = r.x, ylim = r.y)
> ...
> <some fitting>
> ...
> lines(spline(x, <fitted_equation>))
> 
> 
> This gets around the need to manipulate the pars directly and
> hopefully less confusion in reading the code. The key is knowing the
> common ranges of your x and y values in advance.
> 
> Does that help?
> 
> Marc Schwartz
> 
> 
>