Any particular reason you're using I() around your poly()? That
looks weird to me ... and it works fine if you don't do that ... {AND,
I think your result is *incorrect* when you have 3 observations in your
response}.
Basically, you have managed to short-circuit the (admittedly) obscure
machinery that R uses to generate the correct bases when predicting from
new data (see ?makepredictcall ...)
On 3/29/21 6:04 PM, Kenny Bell wrote:
Hi all,
As always, thank you all for your incredible work maintaining and improving
R.
mdl <- lm(data = mtcars,
mpg ~ I(poly(disp, 2)))
predict(mdl, newdata = data.frame(disp = c(120, 120)))
#> Error in poly(disp, 2): 'degree' must be less than number of unique
points
predict(mdl, newdata = data.frame(disp = c(120, 121, 122)))
#> 1 2 3
#> 43.937856 12.617762 3.716257
The predict function seems to require a sufficiently high number of unique
values in newdata when the RHS is a poly. Of course, I would have expected
the output here to be:
#> 1 2
#> 43.937856 43.937856
If people agree, I can submit this to bugzilla.
Kind regards,
Kenny
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