[Rd] xy.coords(MATRIX) bug in code or documentation (PR#8937)

[maechler at stat.math.ethz.ch]

>>>>> "FrPi" == François Pinard <pinard at iro.umontreal.ca>
>>>>>     on Mon, 5 Jun 2006 08:11:20 -0400 writes:

    FrPi> [Martin Maechler]
    >> Thanks a lot, Francois, for your careful reading and
    >> careful report!

    FrPi> Thanks for being receptive! :-)

    FrPi> Another problem in the same area: the documentation
    FrPi> lies about how the function acts when given a
    FrPi> data.frame.  From the code, a data.frame is processed
    FrPi> as if it was a matrix.  From the documentation, while
    FrPi> the data.frame is not mentioned explicitely, it is
    FrPi> implied in the paragraph explaining how a list is
    FrPi> processed (because a data.frame is a list).  Some
    FrPi> reconciliation is needed here as well.

    >> [ Though I do slightly mind the word "lies" since I do
    >> value the 9th commandment..  Not telling the truth
    >> *accidentally* is not "lying" ]

    FrPi> Of course.  You know, I merely forgot a smiley, there.
    FrPi> You are right in that we should try a bit to spare the
    FrPi> extreme susceptibility of some people!  On the other
    FrPi> hand, there should be limits to the feeling that we
    FrPi> are always walking on eggs while writing to R-help or
    FrPi> R-devel, some comfort and happiness is needed, after
    FrPi> all. :-)

    >> Yes; in this case, I propose to just amend the
    >> documentation explainining that data.frames are treated
    >> "as matrices".

    FrPi> Let me add a small comment about data.frames.  It
    FrPi> would be a bit awkward if a data.frame had two columns
    FrPi> "y" and "x" (in that order) and if they were
    FrPi> interpreted differently after matrix coercion.  I
    FrPi> guess the problem would not exist if data.frames were
    FrPi> really interpreted as lists, the "x" and "y" columns
    FrPi> could even appear anywhere (untested).

you are right, but, as I now checked.
in  S  xy.coords() also behaves as it does now in R,
BTW, in both respects {data.frames and ">2-column"  matrices and d.f.s}

Hence --- for back compatibility reasons -- I now tend to agree
with Duncan Murdoch, and would not change xy.coords() behavior
at all, but simply amend the documentation.

Martin