[Rd] Bug in points.formula (PR#6652)

[maechler at stat.math.ethz.ch]

>>>>> "BeT" == Berwin A Turlach <berwin at maths.uwa.edu.au>
>>>>>     on Mon,  8 Mar 2004 09:17:51 +0100 (CET) writes:

    BeT> Dear all, I noticed the following bug in points.formula

    <...>
    BeT> Error in if (length(x) == l) x[s] else x : argument is
    BeT> of length zero

Thank you, Berwin.
The bug is still present in current "R-1.9.0 alpha"
and can be demonstrated with the slightly simpler code

roller <-
    data.frame(weight = c(1.9, 3.1, 3.3, 4.8, 5.3, 6.1, 6.4, 7.6, 9.8, 12.4),
               depression = c(2, 1, 5, 5, 20, 20, 23, 10, 30, 25))
plot( depression ~ weight, data=roller, type="n")
with(roller, points( depression~weight, subset=1:7 )) # ok
with(roller, points( depression~weight, subset=8:10)) # ok
with(roller, points( depression~weight, subset=8:10, col=2))## --> Error

    BeT> This seems to be due to the fact that the data used was
    BeT> attached before the call and not specified in the call
    BeT> via the "data" argument. 

Yes, using "data =" doesn't show the problem,
but as you see, the problem also shows for the more recommended
way of using with() instead of attach()..

    BeT> The following patch seems to fix the problem.

*** /home/berwin/lang/R/Courses/3S6/plot.R.orig	Tue Sep  2 23:43:42 2003
--- /home/berwin/lang/R/Courses/3S6/plot.R	Mon Mar  8 16:06:32 2004
***************
*** 312,318 ****
      mf <- eval(m, parent.frame())
      if (!missing(subset)) {
  	s <- eval(m$subset, data, parent.frame())
! 	l <- nrow(data)
  	dosub <- function(x) if (length(x) == l) x[s] else x
  	dots <- lapply(dots, dosub)
      }
--- 312,320 ----
      mf <- eval(m, parent.frame())
      if (!missing(subset)) {
  	s <- eval(m$subset, data, parent.frame())
!         mtmp <- m
!         mtmp$subset <- NULL
! 	l <- nrow(eval(mtmp, parent.frame()))
  	dosub <- function(x) if (length(x) == l) x[s] else x
  	dots <- lapply(dots, dosub)
      }

-------------------

Yes, but the resulting code becomes even more ugly.
doing a second  eval(m, ..) just with a slightly modified 'm'...

Though I'll have to leave it to others to find if there is a
better patch...

Thanks again, Berwin!
Martin