Dear R-devel,
I recent got a bug report from a locfit user about the use of the subset
argument when calling locfit(). Basically the symptom is that the following
two calls should produce the same result, but they don't:
locfit(y ~ lp(x, h=1), data=subset(dat, x > 1))
locfit(y ~ lp(x, h=1), data=dat, subset= x > 1)
I've tracked the problem down to something shown in the following example, but
have no idea how to get further:
R> x <- 1:5
R> y <- sample(5)
R> m1 <- model.frame(y ~ lp(x))
R> m2 <- model.frame(y ~ lp(x), subset=x>1)
R> class(m1[[2]])
[1] "lp"
R> class(m2[[2]])
[1] "matrix"
So basically model.frame() seems to treat the lp() term differently depending
on whether the subset argument is present or not. Is this supposed to happen?
str(m1) and str(m2) show that besides having one row less and the lp() term
being of class matrix instead of "lp", there's no difference between m1 and m2.
I'd really appreciate it if anyone shed some light on this.
Best,
Andy
Merck Research Labs
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