[R] What does class "call" mean? How do I make class "formula" into a "call"?

[Rita Carreira]

Thank you Bert and Prof. Ripley for your feedback. I did read the language documentation and it was not entirely clear to me, but I'm one of those people that has to read and digest something before it clicks. However, I did realize that the issue with "call"and "formula" was not the real reason why my program did not work. The real reason was much more trivial: I put the arguments inside the systemfit function out of order. Eventually, I figured it out. The good thing about this is that I learned about the existence of the R language documentation. 
Thank you again both!
Rita
=====================================
"If you think education is expensive, try ignorance."--Derek Bok


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> Date: Sat, 25 Jun 2011 05:59:40 +0100
> From: ripley at stats.ox.ac.uk
> To: gunter.berton at gene.com
> CC: ritacarreira at hotmail.com
> Subject: Re: [R] What does class "call" mean? How do I make class "formula" into a "call"?
>
> This is really a misleading subject: it is already a call! From
> ?class
>
> Many R objects have a ‘class’ attribute, a character vector giving
> the names of the classes from which the object _inherits_. If the
> object does not have a class attribute, it has an implicit class,
> ‘"matrix"’, ‘"array"’ or the result of ‘mode(x)’ (except that
> integer vectors have implicit class ‘"integer"’).
>
> So, simply remove the class if you want the mode: but anything which
> needs to know this is call will be looking at the mode and not the
> class.
>
> > zz <- ~x
> > class(zz)
> [1] "formula"
> > mode(zz)
> [1] "call"
>
> And see ?mode and ?call. Formulae and calls which are not formulae
> are completely different: you cannot coerce one to the other.
>
>
> On Fri, 24 Jun 2011, Bert Gunter wrote:
>
> > Well, this is kind of complicated. The first place you should go for
> > help is not this list, but the R docs. Specfically ?call. This
> > assumes familiarity with R's (S3) class system and language structure,
> > however.. For this, I suggest ?UseMethod and consulting the R Language
> > Definition Manual.
> >
> > Perhaps some brave soul on this list will attempt a short explanation
> > in reply. But I am not (s)he.
> >
> > Cheers,
> > Bert
> >
> > Oh -- as for specific suggestions, I think you need to do what the
> > posting guide asks and provide a minimal reproducible example to give
> > people a clearer idea of what's going on.
> >
> > On Fri, Jun 24, 2011 at 2:58 PM, Rita Carreira <ritacarreira at hotmail.com> wrote:
> >>
> >> I have a list called "tabs" that I would like to have the same
> >> structure as my list "eqSystem." The two look like they have the
> >> same format but they are different because when I look at their
> >> attributes, class(eqSystem[[1]]) is "call" but class(tabs[[1]]) is
> >> "formula". I want to have class(tabs[[1]]) as a call too. So what
> >> does "call" mean? And how do I make an object of type "formula" be
> >> of type "call"?
> >> Thank you so much!!!--Rita
> >>> class(tabs)
> >> [1] "list"
> >>> class(tabs[1])
> >> [1] "list"
> >>> class(tabs[[1]])
> >> [1] "formula"> class(eqSystem)
> >> [1] "list"
> >>> class(eqSystem[1])
> >> [1] "list"
> >>> class(eqSystem[[1]])
> >> [1] "call"
> >>
> >>
> >> Rita
> >> =====================================
> >> "If you think education is expensive, try ignorance."--Derek Bok
> >>
> >> ______________________________________________
> >> 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.
> >>
> >
> >
> >
> > --
> > "Men by nature long to get on to the ultimate truths, and will often
> > be impatient with elementary studies or fight shy of them. If it were
> > possible to reach the ultimate truths without the elementary studies
> > usually prefixed to them, these would not be preparatory studies but
> > superfluous diversions."
> >
> > -- Maimonides (1135-1204)
> >
> > Bert Gunter
> > Genentech Nonclinical Biostatistics
> >
> > ______________________________________________
> > 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.
> >
>
> --
> Brian D. Ripley, ripley at stats.ox.ac.uk
> Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
> University of Oxford, Tel: +44 1865 272861 (self)
> 1 South Parks Road, +44 1865 272866 (PA)
> Oxford OX1 3TG, UK Fax: +44 1865 272595