From: Peter Dalgaard <P.Dalgaard_at_biostat.ku.dk>

Date: Wed, 13 Feb 2008 11:18:22 +0100

Date: Wed, 13 Feb 2008 11:18:22 +0100

Berwin A Turlach wrote:

> G'day Peter,

*>
**> On Wed, 13 Feb 2008 08:03:07 +0100
**> Peter Dalgaard <p.dalgaard_at_biostat.ku.dk> wrote:
**>
**>
**>> Ross Boylan wrote:
**>>
**>>> In the following example, the inner evaluation pulls in the global
**>>> value of subset (a function) rather than the one I thought I was
**>>> passing in (a vector). Can anyone help me understand what's going
**>>> on, and what I need to do to fix the problem?
**>>>
**>
**> [...]
**>
**>
**>> The point is that subset (and offset) arguments are subject to the
**>> same evaluation rules as the terms inside the formula: First look in
**>> "data", then in the environment of the formula, which in this case is
**>> the global environment.
**>>
**>
**> Perhaps I have a [senior|blonde]-day today, but this does not seem to
**> be the full explanation about what is going on to me. According to this
**> explanation the following should not work:
**>
**>
**>> lm(Reading~0+Spec+Reader, netto, subset=c(1) )
**>>
**>
**> Call:
**> lm(formula = Reading ~ 0 + Spec + Reader, data = netto, subset = c(1))
**>
**> Coefficients:
**> Spec Reader
**> 1 NA
**>
**> since the value passed to subset is not part of "data" and not in the
**> global environment. But, obviously, it works.
*

It is, however, an expression that can be evaluated in the global environment, and that works.

> OTOH, if we change f0 to

*>
**>
**>> f0
**>>
**> function(formula, data, subset, na.action)
**> {
**> lm(formula, data, subset=subset, na.action=na.action)
**> }
**>
**> then we get the same behaviour as with Ross's use of f1 inside of f0:
**>
**>
**>> t3 <- f0(Reading~0+Spec+Reader, netto, c(1) )
**>>
**> Error in xj[i] : invalid subscript type 'closure'
**>
**>
*

I told you it was elusive... The thing is that lm() is using nonstandard
evaluation, so it sees the _symbol_ subset --- er, wait a minute, too
many "subset"s, let us define it like this instead

f0 <- function(formula, data, s, na.action)
{

lm(formula, data, subset=s, na.action=na.action)
}

Another, I think better, way is

> f0(Reading~0+Spec+Reader, netto, Spec>0 )

Call:

lm(formula = formula, data = data, subset = Spec > 0, na.action = na.action)

Coefficients:

Spec Reader

-1.2976 0.7934

> More over, with the original definition of f0:

*>
**>> f0
**>>
**> function(formula, data, subset, na.action)
**> {
**> f1(formula, data, subset, na.action)
**> }
**>
**>> (f1(Reading~0+Spec+Reader, netto, subset= Spec==1 ))
**>>
**> Reading Spec Reader
**> 1 1 1 1
**>
**>> f0(Reading~0+Spec+Reader, netto, subset= Spec==1 )
**>>
**> Error in xj[i] : invalid subscript type 'closure'
**>
**> Given your explanation, I would have expected this to work.
**>
*

I think the issue here is still that model.matrix ends up being called
with subset=subset rather than subset= Spec==1.

> Reading up on `subset' in ?model.frame also does not seem to shed light

*> onto what is going on.
**>
**> Remaining confused.....
**>
**> Cheers,
**>
**> Berwin
**>
**>
*

-- O__ ---- Peter Dalgaard Ă˜ster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard_at_biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Wed 13 Feb 2008 - 10:24:09 GMT

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