[Rd] I wish xlim=c(0, NA) would work. How about I send you a patch?

Duncan Murdoch murdoch.duncan at gmail.com
Mon Apr 16 20:13:59 CEST 2012

On 12-04-16 1:52 PM, Paul Johnson wrote:
> I'm looking for an R mentor.  I want to propose a change in management
> of plot options xlim and ylim.

Your suggestion sounds reasonable, but because plot limits are such a 
commonly used parameter, it would have to be done quite carefully.  The 
questions I'd ask before implementing it are:

  - Are there other locations besides plot.default where xlim and ylim 
are specified?  I'd like to have them updated consistently.

  - Are there any conflicting uses of NA for a limit in published packages?

  - Which package authors would need to be told about this change, so 
they could make a compatible change?

  - Where does it need to be documented?

Duncan Murdoch

> Did you ever want to change one coordinate in xlim or ylim? It happens
> to me all the time.
> x<- rnorm(100, m=5, s=1)
> y<- rnorm(100, m=6, s=1)
> plot(x,y)
> ## Oh, I want the "y axis" to show above x=0.
> plot(x,y, xlim=c(0, ))
> ##Output: Error in c(0, ) : argument 2 is empty
>   plot(x,y, xlim=c(0,NA ))
> ## Output: Error in plot.window(...) : need finite 'xlim' values
> I wish that plot would let me supply just the min (or max) and then
> calculate the other value where needed.
> It is a little bit tedious for the user to do that for herself.  The
> user must be knowledgeable enough to know where the maximum (MAX) is
> supposed to be, and then supply xlim=c(0, MAX). I can't see any reason
> for insisting users have that deeper understanding of how R calculates
> ranges for plots.
> Suppose the user is allowed to supply NA to signal R should fill in the blanks.
> plot(x,y, xlim=c(0, NA))
> In plot.default now, I find this code to manage xlim
>     xlim<- if (is.null(xlim))
>          range(xy$x[is.finite(xy$x)])
> And I would change it to be something like
>     ##get default range
>     nxlim<- range(xy$x[is.finite(xy$x)])
>     ## if xlim is NULL, so same as current
>      xlim<- if (is.null(xlim)) nxlim
> ## Otherwise, replace NAs in xlim with values from nxlim
>      else xlim[ is.na(xlim) ]<- nxlim[ is.na(xlim) ]
> Who is the responsible party for plot.default.  How about it?
> Think of how much happier users would be!
> pj

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