Re: [Rd] Bug in poly() (PR#11243)

The reason is that you asked for more terms than can exist.

You seem unaware that 2.6.2 is obsolete, and that there are changes in R-patched, with the following NEWS item:

     o poly() has additional checks against user error (as in PR#11243).

and that the help page now says

   degree: the degree of the polynomial. Must be less than the number

           of unique points.

As the FAQ says, please don't make further reports on items that have already been addressed (as clearly marked in the bug repository).

On Fri, 16 May 2008, russell-lenth_at_uiowa.edu wrote:

> I don't understand why this is a bug in usage. Is it because the 2nd
> argument is not named? I get the same behavior if I do name it:
>
> =====
> [R version 2.6.2 (2008-02-08), Windows XP Pro]
>
> R> x = rep(1:4,3)
> R> y = (1:12)^1.5
> R> lm(y ~ poly(x, degree=10))
>
> Call:
> lm(formula = y ~ poly(x, degree = 10))
>
> Coefficients:
> (Intercept) poly(x, degree = 10)1 poly(x, degree = 10)2
> 18.39370 14.21385 0.58588
> poly(x, degree = 10)3 poly(x, degree = 10)4 poly(x, degree = 10)5
> -0.01770 3.34767 -11.46388
> poly(x, degree = 10)6 poly(x, degree = 10)7 poly(x, degree = 10)8
> 0.51178 0.44296 12.47199
> poly(x, degree = 10)9 poly(x, degree = 10)10
> -28.38972 18.47439
> =====
>
> Is there a case where we *would* want a 10th degree polynomial fitted to
> only 4 distinct x values? A simple modification [changing 'length(x)'
> to 'length(unique(x))' in 2 places] seems to fix this:
> =====
> R> mypoly
> ...
> if (raw) {
> if (degree >= length(unique(x)))
> stop("'degree' must be less than number of points")
> ...
> if (is.null(coefs)) {
> if (degree >= length(unique(x)))
> stop("'degree' must be less than number of points")
> ...
>
> R> lm(y ~ mypoly(x, degree=10))
> Error in mypoly(x, degree = 10) :
> 'degree' must be less than number of points
> =====
>
> Russ
> --
> Russell V. Lenth, Professor
> Department of Statistics
> & Actuarial Science (319)335-0814 FAX (319)335-3017
> The University of Iowa russell-lenth_at_uiowa.edu
> Iowa City, IA 52242 USA http://www.stat.uiowa.edu/~rlenth/
>
> ______________________________________________
> R-devel_at_r-project.org mailing list
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>

-- 
Brian D. Ripley,                  ripley_at_stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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