From ted.harding at nessie.mcc.ac.uk  Mon Jul 16 16:40:40 2007
From: ted.harding at nessie.mcc.ac.uk ( (Ted Harding))
Date: Mon, 16 Jul 2007 15:40:40 +0100 (BST)
Subject: [Rd] formula(CO2)
In-Reply-To: <971536df0707160716i7084039cp48560beb367fa141@mail.gmail.com>
Message-ID: <XFMail.070716154040.ted.harding@nessie.mcc.ac.uk>

On 16-Jul-07 14:16:10, Gabor Grothendieck wrote:
> Following up on your comments it seems formula.data.frame just creates
> a formula whose lhs is the first column name and whose rhs is made up
> of the remaining column names.  It ignores the "formula" attribute.
> 
> In fact, CO2 does have a formula attribute but its not extracted by
> formula.data.frame:
> 
>> CO2 at formula
> uptake ~ conc | Plant
>> formula(CO2)
> Plant ~ Type + Treatment + conc + uptake

Indeed! And, following up yet again on my own follow-up comment:

library(combinat)

for(j in (1:4)){
  for(i in combn((1:4),j,simplify=FALSE)){
    print(formula(CO2[,c(5,i)]))
  }
}
uptake ~ Plant
uptake ~ Type
uptake ~ Treatment
uptake ~ conc
uptake ~ Plant + Type
uptake ~ Plant + Treatment
uptake ~ Plant + conc
uptake ~ Type + Treatment
uptake ~ Type + conc
uptake ~ Treatment + conc
uptake ~ Plant + Type + Treatment
uptake ~ Plant + Type + conc
uptake ~ Plant + Treatment + conc
uptake ~ Type + Treatment + conc
uptake ~ Plant + Type + Treatment + conc

opening the door to automated fitting of all possible models
(without interactions)!

Now if only I could find out how to do the interactions as well,
I would never need to think again!

best wishes,
Ted.

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Date: 16-Jul-07                                       Time: 15:40:36
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[Rd] formula(CO2)
 (Ted Harding