Suggestion for qqplot() improvement

[Martin Maechler]

>>>>> On Tue, 31 Aug 1999 14:57, Werner Stahel <stahel@stat.math.ethz.ch> said:

    WSt> Here is a suggestion.  It seems that qqplots, comparing a sample
    WSt> to a distribution other than the normal, are not explicitly
    WSt> available in S or R. I found

(in S-plus / Trellis it is, see below)

    WSt>	   qqplot(y, rt(300, df = 5))

    WSt> as an example in the help file to  qqplot .
    WSt> This is not very sensible. 

(it only tried to show that you can QQ-plot two datasets 
 of *different* length, rather than anything else)

    WSt> I would prefer

    WSt>   n <- length(y)
    WSt>   qqplot(qt((1:n)/(n+1), df=5), y, xlab='quantiles', ylab='data')

yes, for comparison with a theoretical distribution.

Maybe even
      qqplot(qt(ppoints(n), df=5), y, 
	     xlab='quantiles of t(* ,df=5)', ylab='data')

    WSt> and this could be shortened to

    WSt>   qqplot(y, distribution='t', df=5)

    WSt> with an easy extension of the function.

I found:

   Trellis in S-plus has
	    qqmath(formula, distribution = qnorm, f.value = ppoints, ...),
   for your example
        qqmath( ~ y, distribution = function(p) qt(p, df=5), ...)

which is slightly more general (also works with panels, banking to 45
deg,..) but quite a bit more complicated to use for non-sophisticated users.

What should we do / would we want for R?

Martin
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-devel-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._