[Rd] Improvements (?) in stats::poly and stats::polym.

[Martin Maechler]

>>>>> "MM" == Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>     on Fri, 17 Jul 2015 18:00:28 +0200 writes:

    MM> Dear Keith,
>>>>>   <Keith.Jewell at campdenbri.co.uk>
>>>>>     on Thu, 16 Jul 2015 08:58:11 +0000 writes:

    >> Dear R Core Team,
    >> Last week I made a post to the R-help mailing list
    >> “predict.poly for multivariate data”
    >> <https://stat.ethz.ch/pipermail/r-help/2015-July/430311.html>
    >> but it has had no responses so I’m sending this to the
    >> email address of package:stats maintainer. Please feel
    >> free to tell me that this is inappropriate.

    MM> Asking R Core in your case is ok ...
    MM> { though still slightly "sub optimal" (but *not* "inappropriate"!):
    MM> Ideallly you'd have followed the posting guide
    MM> (http://www.r-project.org/posting-guide.html) here,
    MM> namely to send your original post to R-devel instead of R-help.
    MM> Then it would have been noticed by me and most probably
    MM> several other R core members ...
    MM> }

    >> IMHO the reproducible code I presented in that post:
    >> #############
    >> library(datasets)
    >> alm <- lm(stack.loss ~ poly(Air.Flow, Water.Temp, degree=3), stackloss)
    >> alm$fitted.values[1:10]   # "correct" prediction values [1:10]
    >> predict(alm, stackloss)[1:10]  #  gives correct values
    >> predict(alm, stackloss[1:10,]) #  gives wrong values
    >> #########
    >> ... clearly demonstrates something wrong, the two predicts should not differ.

    >> I hesitate to call it a bug, it might be viewed as inappropriate usage. But it's easy to get wrong answers, fairly small changes to poly and polym correct the wrongness, and I think the changes are backwards compatible. Perhaps appending the altered codes made the R-help post too long for easy comprehension, I attach them to this email.

    MM> Thank you!

    MM> I had started to look at your R-help post and noticed that you
    MM> changed the *printout* of the R functions, instead of the
    MM> source 
    MM> The current development version of that part of the R
    MM> source code is always at
    MM> https://svn.r-project.org/R/trunk/src/library/stats/R/contr.poly.R

    MM> and if you look carefully, you see that there are comments in
    MM> the sources that are lost in the process (of parsing,
    MM> byte-compiling, saving in binary, ....),
    MM> but never mind:
    MM> you've marked your changes well and I can use your version to
    MM> modify the sources.

    >> From what I've understood, the changes make much sense and look
    MM> good; and if no problem surfaces should make it into R - with an
    MM> acknowledgement to you, of course.

I've now committed corresponding changes to R-devel, changes
which indeed have evolved from your (Keith) contributions, thank
you very much.  My additional changes were trying to slightly simplify
the code logic, (and a new argument 'simple' to gain some
speed).

If the changes do not have visible negative effects on existing
CRAN/Bioconductor code (which *is* possible, after all, the results now sometimes
are different in the attributes),
we may consider porting the changes to 'R 3.2.1 patched' which
will become  R 3.2.2 in three weeks.

Thank you again,
Martin Maechler

    
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