From ted.harding at nessie.mcc.ac.uk  Mon Jul 16 15:57:56 2007
From: ted.harding at nessie.mcc.ac.uk ( (Ted Harding))
Date: Mon, 16 Jul 2007 14:57:56 +0100 (BST)
Subject: [Rd] formula(CO2)
In-Reply-To: <971536df0707160628g37e301e1wf81eaee0b7feb841@mail.gmail.com>
Message-ID: <XFMail.070716145756.ted.harding@nessie.mcc.ac.uk>

On 16-Jul-07 13:28:50, Gabor Grothendieck wrote:
> The formula attribute of the builtin CO2 dataset seems a bit strange:
> 
>> formula(CO2)
> Plant ~ Type + Treatment + conc + uptake
> 
> What is one supposed to do with that?  Certainly its not suitable
> for input to lm and none of the examples in ?CO2 use the above.

I think one is supposed to ignore it! (Or maybe be inspired to
write a mail to the list ... ).

I couldn't find anything that looked like the above formula from
str(CO2). But I did spot that the order of terms in the formula:
Plant, Type, treatment, conc, uptake, is the same as the order
of the "columns" in the dataframe.

So I tried:

  D<-data.frame(x=(1:10),y=(1:10))

  formula(D)
  x ~ y

So, lo and behold, D has a formula!

Or does it? Maybe if you give formula() a dataframe, it simply
constructs one from the "columns".

Best wishes,
Ted.

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Date: 16-Jul-07                                       Time: 14:57:28
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[Rd] formula(CO2)
 (Ted Harding