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

   lm(freeny)

On Sun, Nov 29, 2009 at 8:49 AM, Matthieu Stigler 
<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