I think the worst aspect of this restriction in poly() is that when you use poly in the formula of a model-fitting function you cannot have any missing values in the data, even if you supply na.action=na.exclude.
> d <- transform(data.frame(y=c(-1,1:10)), x=log(y)) Warning message: In log(y) : NaNs produced > fit <- lm(y ~ poly(x, 3), data=d, na.action=na.exclude) Error in poly(x, 3) : missing values are not allowed in 'poly' Thus people are pushed to using a less stable formulation like > fit <- lm(y ~ x + I(x^2) + I(x^3), data=d, na.action=na.exclude) Bill Dunlap TIBCO Software wdunlap tibco.com On Wed, Mar 23, 2016 at 12:59 PM, Liviu Andronic <landronim...@gmail.com> wrote: > Dear all, > I'm a bit surprised by this behavior in poly: > > x <- c(NA, 1:10) > poly(x, degree = 2, raw=TRUE) > ## Error in poly(x, degree = 2, raw = TRUE) : > ## missing values are not allowed in 'poly' > x^2 > ## [1] NA 1 4 9 16 25 36 49 64 81 100 > > As you can see, poly() will fail if the vector contains NAs, whereas > it is perfectly possible to obtain the square of the vector manually. > > Is there a reason for this limitation in poly? > > Regards, > Liviu > > > -- > Do you think you know what math is? > http://www.ideasroadshow.com/issues/ian-stewart-2013-08-02 > Or what it means to be intelligent? > http://www.ideasroadshow.com/issues/john-duncan-2013-08-30 > Think again: > http://www.ideasroadshow.com/library > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
