[R] lm: eval(parse(text=)) works on one side y/x but not on both?

[Matthieu Stigler]

Gabor Grothendieck a écrit :
> Try this:
>
> ix <- 1:2
> lm(as.matrix(freeny[ix]) ~., freeny[-ix])
>
clean and clever!!! Thanks a lot!! You really simplified the code!!!

Just for curiosity, do you see why parse(eval)) was not working twice in 
same formula?

thanks a lot!!

Matthieu
>
> On Sun, Nov 29, 2009 at 8:56 AM, Matthieu Stigler 
> <matthieu.stigler at gmail.com <mailto:matthieu.stigler at gmail.com>> wrote:
>
>     Thanks for answering so fast!!
>
>
>           lm(freeny)
>
>     :-)
>     Ok that's working for the one equation case :-) Was example case...
>
>     But now I want to have not only first column of freeny on the left
>     but both first? And I don't know their names a priori...
>
>     Thanks!
>
>
>         On Sun, Nov 29, 2009 at 8:49 AM, Matthieu Stigler
>         <matthieu.stigler at gmail.com
>         <mailto:matthieu.stigler at gmail.com>
>         <mailto:matthieu.stigler at gmail.com
>         <mailto:matthieu.stigler at 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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