[Rd] Bug in all.equal() or in the plm package

[Arne Henningsen]

Hi!

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():

======================================
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