[R] verInd= and HorInd= arguments to pairs() function

[Martin Maechler]

>>>>> Gerrit Eichner 
>>>>>     on Fri, 8 Jun 2018 12:55:31 +0200 writes:

    > Am 08.06.2018 um 12:02 schrieb Martin Maechler:
    >>>>>>> Martin Maechler
    >>>>>>> on Fri, 8 Jun 2018 11:13:24 +0200 writes:
    >> 
    >> [..........]
    >> 
    >> >> Thank you, Chris, for the report and
    >> >> Gerrit for your proposed fix !!
    >> >>
    >> >> It looks good to me,  but I will test some more (also with
    >> >> 'row1attop=FALSE')  before committing the bug fix.
    >> 
    >> > and there, another change was needed:  Instead of your
    >> 
    >> > for (j in if (row1attop) verInd else rev(verInd))
    >> >    for (i in horInd) {
    >> 
    >> > we do now need
    >> 
    >> > for(j in verInd)
    >> >    for(i in if(row1attop) horInd else rev(horInd)) {
    >> 
    >> > and the difference is of course only relevant for the
    >> > non-default  'row1attop = FALSE'
    >> 
    >> > (which some graphic experts argue to be clearly *better* than the default,
    >> > as only in that case,  the upper and lower triangles of the
    >> > matrix are nicely "mirrors of each other", and that is also
    >> > the reason why  lattice::splom()  uses the equivalent of
    >> > 'row1attop=FALSE')
    >> 
    >> > I will commit the change to R-devel today - and intend to port
    >> > to R-patched in time to make it into the upcoming R 3.5.1.
    >> 
    >> Well, as I find, there are more bugs there, if you are using
    >> 'horInd' and 'verInd' creatively:
    >> 
    >> In a nice pairs(), the axis ticks (and their labels (numbers))
    >> are always "on the outside" of the scatterplot matrix, and
    >> nicely alternating.  This is not the case unfortunately, when using
    >> horInd or verInd which are *not* of the form p1:p2 (p1 <= p2)
    >> 
    >> ==> even more changes are needed to make these cases "nice",

    > Well, the *shown* axis ticks and labels do nicely alternate if
    > (hor|ver)Ind = p1:p2 (p1 <= p2) is fulfilled, but not all of
    > the axis ticks and labels, which one *might* wish to see, are
    > currently drawn anyway ... I would consider changes which "heal"
    > this as more interesting than solving this problem in full
    > generality, i.e., in cases of creative use of (hor|ver)Ind.
    > However, I don't think it's urgent, at all.


    >> or  should we *require* horInd and verInd to be of that form??
    >> 
    >> This would not be back-compatible, but than such cases have been
    >> "wrong" really in all versions of R anyway, *and*  at least be
    >> reordering the matrix/data.frame columns, the restriction of
    >> 
    >> (hor|ver)Ind =  p1:p2 (p1 <= p2)
    >> 
    >> would seem acceptable, would it ?
    >> 

    > I could live very well with that requirement (while breaking
    > back-compatibility), because from my point of view a "creative"
    > use of 'horInd' and 'verInd' violating (hor|ver)Ind = p1:p2
    > (p1 <= p2) won't occur often.

    > On the other hand, why forcing (hor|ver)Ind = p1:p2 (p1 <= p2)?
    > If people violated it "they get what they deserve". ;-)

    > Btw, 'horInd' and 'verInd' sort of exchange their meaning if
    > row1attop = FALSE, but I this can be explained by the "work flow":
    > First, (hor|ver)Ind are used to select the respective rows and
    > columns from the full paris-plot, and then, row1attop is used
    > when the results are drawn. I think this is sensible.

Thank you; and yes indeed, and I was not going to change that.

In fact, I've found a relatively nice solution now, which does
*not* restrict the settings of '{hor,ver}Ind' and fixes all
problems mentioned,  quite back compatibly, and in some sense
perfectly labeling the axes.

==> Committed to R-devel svn c74871  a few minutes ago.

Martin