[Rd] pch=NA (PR#7737)

[arnima at u.washington.edu]

I'd like to suggest changes to three help pages, regarding the use of 
pch=NA to suppress plotting symbols. See below.

Arni

R 2.0.1 on WinXP



===
help(bxp)
===

The argument outpch=" " needs to be replaced with outpch=NA in two places.

I actually wrote this part of the documentation myself at one point, but 
have now realized that pch=NA and pch=" " are not the same:

   x <- split(rlnorm(26e4), letters)
   ## NA generates small file
   postscript("na.ps");    boxplot(x,outpch=NA);  dev.off()
   ## Space generates large file
   postscript("space.ps"); boxplot(x,outpch=" "); dev.off()



===
help(par)
help(points)
===

Please specify that pch=NA can be used to suppress plotting symbols.

I'm aware of type="n", but pch=NA can be a useful feature inside functions 
and should be documented somewhere. Other negative-sounding values 
(-1,0,NULL,""," ") generate different results, and only pch=NA does the 
job properly.