R help - Nov 2009 - lm: eval(parse(text=)) works on one side y/x but not on both?

Hi

My goal is to do a (multiple) regression, just knowing that my Y 
variables will be the say k first variables of a matrix/data frame. I 
thought I should do it with eval(parse)) but encounter a strange problem.

See:
lm(y~.-y, data=freeny) #that's what I want to do in the one equation case
#Problem is I don't know name of the variable... only that it is the 
first one...
#so idea is to just take first name
a<-colnames(freeny)
#and then use eval(parse(text=a[1]))

#it works if I replace y on either the left or right side:
lm(eval(parse(text=a[1]))~.-y, data=freeny) #does the same
lm(y~.-eval(parse(text=a[1])), data=freeny)

#but not if I do this call twice:
lm(eval(parse(text=a[1]))~.-eval(parse(text=a[1])), data=freeny)
#variable I wanted to remove (y) ist still there

Do you understand why I can call eval(parse) only once? Should I try a 
update workaround? Or have idea of any other solution? Maybe there is 
something much simpler I'm missing:-(

Thanks a lot!!!

Matthieu Stigler

Try this:

   lm(freeny)

On Sun, Nov 29, 2009 at 8:49 AM, Matthieu Stigler <
matthieu.stigler@gmail.com> wrote:
> Hi
>
> My goal is to do a (multiple) regression, just knowing that my Y variables
> will be the say k first variables of a matrix/data frame. I thought I
should
> do it with eval(parse)) but encounter a strange problem.
>
> See:
> lm(y~.-y, data=freeny) #that's what I want to do in the one equation
case
> #Problem is I don't know name of the variable... only that it is the
first
> one...
> #so idea is to just take first name
> a<-colnames(freeny)
> #and then use eval(parse(text=a[1]))
>
> #it works if I replace y on either the left or right side:
> lm(eval(parse(text=a[1]))~.-y, data=freeny) #does the same
> lm(y~.-eval(parse(text=a[1])), data=freeny)
>
> #but not if I do this call twice:
> lm(eval(parse(text=a[1]))~.-eval(parse(text=a[1])), data=freeny)
> #variable I wanted to remove (y) ist still there
>
> Do you understand why I can call eval(parse) only once? Should I try a
> update workaround? Or have idea of any other solution? Maybe there is
> something much simpler I'm missing:-(
>
> Thanks a lot!!!
>
> Matthieu Stigler
>
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