> -----Original Message-----
> From: r-devel-boun...@r-project.org [mailto:r-devel-boun...@r-
> project.org] On Behalf Of Arne Henningsen
> Sent: Tuesday, November 10, 2009 2:24 AM
> To: Duncan Murdoch; r-devel@r-project.org; Yves Croissant;
> giovanni_mi...@generali.com; Achim Zeileis
> Subject: Re: [Rd] Bug in all.equal() or in the plm package
>
> On Mon, Nov 9, 2009 at 12:24 PM, Duncan Murdoch <murd...@stats.uwo.ca>
> wrote:
> > Arne Henningsen wrote:
> >>
> >> I noticed that there is a (minor) bug either the command all.equal()
> >> or in the "plm" package. I demonstrate this using an example taken
> >> from the documentation of plm():
> >>
> >
> > I'm not sure this is a bug, but I'd call it at least a design flaw.
> The
> > problem is that the length.Formula method in the Formula package
> (which plm
> > depends on) returns a vector of length 2. Now there's nothing in R
> that
> > requires length() to return a scalar,
No, but outside of R, length is a one dimensional real number
except perhaps in some esoteric mathematics, so I'm puzzled
why length in R would be redefined to produce non-scalars.
> >but all.equal assumes it does,
> and I'd
> > guess there are lots of other places this assumption is made.
>
> Okay, let's call it "design flaw". Given that the "unusual" behaviour
> of length.Formula() causes this problem, I suggest that the
> length.Formula() method should be changed. Maybe to something like
>
> R> a <- as.Formula( y ~ x | z | w )
> # current behaviour:
> R> length(a)
> [1] 1 3
> # suggested behaviour:
> R> length(a)
> [1] 2
> R> length(a[[1]])
> [1] 1
> R> length(a[[2]])
> [1] 3
>
How about
# Total number of variables in model
R> length(a)
[1] 4
# Predictor variables (on the right hand side) pred(a) or rhs(a)
R> length(pred(a))
[1] 3
# Response variables (on the left hand side) resp(a) or lhs(a)
R> length(resp(a))
[1] 1
so all lengths of a formula's components can
be obtained as scalars.
R> length(a)
[1] 3
is what R 2.9.1 produced, and may often be what is expected
for the length of a formula, so the above could be
# Total number of variables in model
R> length(total(a))
[1] 4
# Predictor variables (on the right hand side) pred(a) or rhs(a)
R> length(a)
[1] 3
# Response variables (on the left hand side) resp(a) or lhs(a)
R> length(resp(a))
[1] 1
Steve McKinney
> This would be more consistent with the usual behaviour of length, e.g.
> R> b <- list( 1, 1:3 )
> R> length(b)
> [1] 2
> R> length(b[[1]])
> [1] 1
> R> length(b[[2]])
> [1] 3
>
> /Arne
>
>
> >> ======================================
> >> R> data("Produc", package="plm")
> >> R> zz <- plm(log(gsp)~log(pcap)+log(pc)+log(emp)+unemp,
> >> + data=Produc, index=c("state","year"))
> >> R> all.equal(zz,zz)
> >> [1] TRUE
> >> Warning message:
> >> In if (length(target) != length(current)) return(paste("target,
> >> current differ in having response: ", :
> >> the condition has length > 1 and only the first element will be
> used
> >>
> >>>
> >>> all.equal(zz$formula,zz$formula)
> >>>
> >>
> >> [1] TRUE
> >> Warning message:
> >> In if (length(target) != length(current)) return(paste("target,
> >> current differ in having response: ", :
> >> the condition has length > 1 and only the first element will be
> used
> >>
> >>>
> >>> class(zz$formula)
> >>>
> >>
> >> [1] "pFormula" "Formula" "formula"
> >> ======================================
> >>
> >> The last commands show that the warning message comes from comparing
> >> the elements "formula", which are of the class "pFormula"
> (inheriting
> >> from "Formula" and "formula"). It would be great if this issue could
> >> be fixed in the future.
> >>
> >> Thanks a lot,
> >> Arne
>
> --
> Arne Henningsen
> http://www.arne-henningsen.name
>
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