R devel - Feb 2003 - unique turns ordered into factor (PR#2591)

[reported originally by Christoffer Tornøe]
> f <- ordered(month.name)
> f
 [1] January   February  March     April     May       June      July
 [8] August    September October   November  December
12 Levels: April < August < December < February < January < July
< ... < September
> unique(f)
 [1] January   February  March     April     May       June      July
 [8] August    September October   November  December
12 Levels: April August December February January July June March ... September

this causes trouble in the internals of panel.superpose if the groups
argument is an ordered factor. In that case

           id <- (groups[subscripts] == vals[i])

gives off the warning

Incompatible methods ("Ops.ordered", "Ops.factor") for
"=="

S-PLUS (6.0 at least) does not do this, so I assume the fix is to
modify unique.default in the obvious way.

[Still present in the development sources]

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907

>>>>> "PD" == p dalgaard
<p.dalgaard@biostat.ku.dk>
>>>>>     on Fri, 28 Feb 2003 15:58:02 +0100 (MET) writes:
    PD> [reported originally by Christoffer Tornøe]
    >> f <- ordered(month.name)
    >> f
    PD> [1] January   February  March     April     May       June      July
    PD> [8] August    September October   November  December
    PD> 12 Levels: April < August < December < February < January
< July < ... < September

    >> unique(f)
    PD> [1] January   February  March     April     May       June      July
    PD> [8] August    September October   November  December
    PD> 12 Levels: April August December February January July June March ...
September

    PD> this causes trouble in the internals of panel.superpose if the groups
    PD> argument is an ordered factor. In that case

    PD> id <- (groups[subscripts] == vals[i])

    PD> gives off the warning

    PD> Incompatible methods ("Ops.ordered",
"Ops.factor") for "=="

    PD> S-PLUS (6.0 at least) does not do this, so I assume the fix is to
    PD> modify unique.default in the obvious way.

I think it's a clear bug (independently of other implementations ..)
Maybe it would be a bit cleaner to write an unique.factor().
The current unique.default() stems from the pre-method time,
i.e., when it was just unique().

    PD> [Still present in the development sources]

Martin