[R-sig-ME] [R] understanding I() in lmer formula

[Don Cohen]

 > The expression `~z.n.males` is a unary formula, i.e. a language
 > object, so it's not a data object much less a numeric data
 > object. The `*` operator does not have a method for such an object
 > as the second argument.

ok, so the next question is where this comes from

 > It appears that trying to use I() on an expression with a
 > multiplication operator was not something that was anticipated as
 > having a sensible meaning.

That would cause it to get the error in all those other cases where
there is no error.
Notice that the difference between getting the error and not getting
it is not in the I() term - that's the same in both cases.

 > I'm not sure what this was supposed to be doing but perhaps you
 > wanted the interaction()-function rather than the as.is function?

What all this is supposed to mean is another topic I'd also like to
discuss.  I did not write the original formula.  I'm just trying to
make small changes to it to see the effects.  Or at least I WAS trying
to make small changes.  I had already made rather large changes to
simplify the example in my first post.

I think this shows that the problem is in parsing:
 parse <- lFormula(formula = log.corti~z.n.fert.females*z.n.males+
          is.alpha2*(z.infanticide.susceptibility+z.min.co.res+z.co.res+z.log.tenure)+
          z.xtime+z.age.at.sample+sin.season+cos.season+
          (1 #+z.n.fert.females
           +z.n.males
           +is.alpha2.subordinate
           +z.infanticide.susceptibility
           +z.min.co.res
           +z.log.tenure
           +z.co.res
           # +z.xtime
           +z.age.at.sample
           +sin.season
           +cos.season+
                I(z.n.fert.females*z.n.males)+
                        I(is.alpha2.subordinate*z.min.co.res)+
              #  I(z.co.res*is.alpha2.subordinate)
                I(is.alpha2.subordinate*z.co.res)
              #  +int.is.a.log.ten
                ||monkeyid), data=fe.re.xx$data)
+ + + + + + + + + + + + + + + + + + + Error in is.alpha2.subordinate * ~z.co.res : 
  non-numeric argument to binary operator

whereas switching the order of the * arguments
parse <- lFormula(formula = log.corti~z.n.fert.females*z.n.males+
          is.alpha2*(z.infanticide.susceptibility+z.min.co.res+z.co.res+z.log.tenure)+
          z.xtime+z.age.at.sample+sin.season+cos.season+
          (1 #+z.n.fert.females
           +z.n.males
           +is.alpha2.subordinate
           +z.infanticide.susceptibility
           +z.min.co.res
           +z.log.tenure
           +z.co.res
           # +z.xtime
           +z.age.at.sample
           +sin.season
           +cos.season+
                I(z.n.fert.females*z.n.males)+
                        I(is.alpha2.subordinate*z.min.co.res)+
               I(z.co.res*is.alpha2.subordinate)
              #  I(is.alpha2.subordinate*z.co.res)
              #  +int.is.a.log.ten
                ||monkeyid), data=fe.re.xx$data)
+ + + + + + + + + + + + + + + + + + + > 
> parse$formula
log.corti ~ z.n.fert.females * z.n.males + is.alpha2 * (z.infanticide.susceptibility + 
    z.min.co.res + z.co.res + z.log.tenure) + z.xtime + z.age.at.sample + 
    sin.season + cos.season + ((1 | monkeyid) + (0 + z.n.males | 
    monkeyid) + (0 + is.alpha2.subordinate | monkeyid) + (0 + 
    z.infanticide.susceptibility | monkeyid) + (0 + z.min.co.res | 
    monkeyid) + (0 + z.log.tenure | monkeyid) + (0 + z.co.res | 
    monkeyid) + (0 + z.age.at.sample | monkeyid) + (0 + sin.season | 
    monkeyid) + (0 + cos.season | monkeyid) + (0 + I(z.n.fert.females * 
    z.n.males) | monkeyid) + (0 + I(is.alpha2.subordinate * z.min.co.res) | 
    monkeyid) + (0 + I(z.co.res * is.alpha2.subordinate) | monkeyid))

BTW, passing that result to lFormula with the
I(z.co.res * is.alpha2.subordinate) changed to
I(is.alpha2.subordinate * z.co.res )
also works.

So as a work around perhaps the solution is to start from the result
of lFormula on the original formula and make my incremental changes
to that.