scoping error in xy.coords (PR#932)

Hola!

rm(list=ls(all=TRUE))

x <- 1:20
y <- 1+x+rnorm(x)

xy.coords(y  ~ x,NULL)

... expected output, correct, but when called from inside lowess:

  lowess(y ~ x)

Error in xy.coords(x, y) : x and y lengths differ

If you don't call them x and y it works

x<-1:10
y<-1:10
lowess(y~x)

Error in xy.coords(x, y) : x and y lengths differ

z<-y
w<-x
lowess(z~w)

$x
 [1]  1  2  3  4  5  6  7  8  9 10

$y
 [1]  1  2  3  4  5  6  7  8  9 10

The problem is that the formula is evaluated in the parent frame, where y
evaluates to NULL, and x evaluates to y~x, rather than in the global
environment where they would both evaluate to vectors.

In order to handle formulas correctly I think xy.coords needs to use the
same sort of indirect evaluation as model.frame: eg
   xy <-substitute(xy.coords(X,Y),list(X=substitute(x),Y=substitute(y)))
   xy<-eval(xy,parent.frame())
works as a replacement for the first two lines of lowess().  I hadn't
realised that xy.coords() was supposed to handle formulas, and since it
doesn't have a data= argument it can't do it very well.

This seems a bit drastic, given the number of times xy.coords is used.
Perhaps there's a simpler solution.


	-thomas

Thomas Lumley			Asst. Professor, Biostatistics
tlumley@u.washington.edu	University of Washington, Seattle
^^^^^^^^^^^^^^^^^^^^^^^^
 NOTE NEW EMAIL ADDRESS

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
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
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Thomas Lumley <tlumley@u.washington.edu> writes:

evaluates to NULL, and x evaluates to y~x, rather than in the global
environment where they would both evaluate to vectors.

In order to handle formulas correctly I think xy.coords needs to use the
same sort of indirect evaluation as model.frame: eg
   xy <-substitute(xy.coords(X,Y),list(X=substitute(x),Y=substitute(y)))
   xy<-eval(xy,parent.frame())
works as a replacement for the first two lines of lowess().  I hadn't
realised that xy.coords() was supposed to handle formulas, and since it
doesn't have a data= argument it can't do it very well.

This seems a bit drastic, given the number of times xy.coords is used.
Perhaps there's a simpler solution.

Perhaps use the new formula environments in xy.coords? Seems to work


        if (inherits(x, "formula") && length(x) == 3) {
            ylab <- deparse(x[[2]])
            xlab <- deparse(x[[3]])
            y <- eval(x[[2]], environment(x), parent.frame())
            x <- eval(x[[3]], environment(x), parent.frame())
	}

O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
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
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Perhaps use the new formula environments in xy.coords? Seems to work

Yes, much better.

	-thomas

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
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
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._