[Rd] ftable <-> data.frame etc {was "justify hard coded in format.ftable"}

[Martin Maechler]

>>>>> Gabor Grothendieck 
>>>>>     on Thu, 14 May 2020 06:56:06 -0400 writes:

> If you are looking at ftable could you also consider adding
> a way to convert an ftable into a usable data.frame such as
> the ftable2df function defined here:

> https://stackoverflow.com/questions/11141406/reshaping-an-array-to-data-frame/11143126#11143126

> and there is an example of using it here:

> https://stackoverflow.com/questions/61333663/manipulating-an-array-into-a-data-frame-in-base-r/61334756#61334756

> Being able to move back and forth between various base class representations
> seems like something that would be natural to provide.

Sure!

But there is already an  as.data.frame() method for "ftable",
{and I would not want the    if(! .. ftable)  ftable(x)  part anyway.

What I think many useRs / programmeRs  very often forget about
is more-than-2-dimensional arrays {which *are* at the beginning
of that SO question} and that these are often by far the most
efficient data structure (rather than the corresponding data frames).  

and even less people forget that a "table" in base R is just a
special case of a 1-D, 2-D, 3-D, .... array.
(Semantically a special case: "array" with non-negative integer content 

I'd claim that everything you here ("move back and forth between
...") is already there in the "ftable" implementation in stats,
notably in the source file  src/library/stats/R/ftable.R
 -> https://svn.r-project.org/R/trunk/src/library/stats/R/ftable.R

The problem may be in

1) too sparse documentation about the close relations
   "ftable" <-> "array" <-> "table" <-> "data.frame" 

2) people not thinking often enough about more-than-2D-arrays and the
  special corresponding class "table" in R.

To start with one:

> str(UCBAdmissions)
 'table' num [1:2, 1:2, 1:6] 512 313 89 19 353 207 17 8 120 205 ...
 - attr(*, "dimnames")=List of 3
  ..$ Admit : chr [1:2] "Admitted" "Rejected"
  ..$ Gender: chr [1:2] "Male" "Female"
  ..$ Dept  : chr [1:6] "A" "B" "C" "D" ...
>

and look at the *examples* in the help files and the S3 methods

methods(class = "ftable")
[1] as.data.frame as.matrix     as.table      format        head          print        
[7] tail         
see '?methods' for accessing help and source code
> methods(class = "table")
 [1] [             aperm         as.data.frame Axis          coerce        initialize   
 [7] lines         plot          points        print         show          slotsFromS3  
[13] summary       tail         
see '?methods' for accessing help and source code
> 

... need to close now, there's more to be said ...



    > On Thu, May 14, 2020 at 5:32 AM Martin Maechler
    > <maechler using stat.math.ethz.ch> wrote:
    >> 
    >> >>>>> SOEIRO Thomas
    >> >>>>>     on Wed, 13 May 2020 20:27:15 +0000 writes:
    >> 
    >> > Dear all,
    >> > I haven't received any feedback so far on my proposal to make "justify" argument available in stats:::format.ftable
    >> 
    >> > Is this list the appropriate place for this kind of proposal?
    >> 
    >> Yes, it is.. Actually such a post is even a "role model" post
    >> for R-devel.
    >> 
    >> > I hope this follow-up to my message won't be taken as rude. Of course it's not meant to be, but I'm not used to the R mailing lists...
    >> 
    >> well, there could be said much, and many stories told here ... ;-)
    >> 
    >> > Thank you in advance for your comments,
    >> 
    >> > Best,
    >> > Thomas
    >> 
    >> The main reasons for "no reaction" (for such nice post) probably
    >> are combination of the following
    >> 
    >> - we are busy
    >> - if we have time, we think other things are more exciting
    >> - we have not used ftable much/at all and are not interested.
    >> 
    >> Even though the first 2 apply to me, I'll have a 2nd look into
    >> your post now, and may end up well agreeing with your proposal.
    >> 
    >> Martin Maechler
    >> ETH Zurich  and  R Core team
    >> 
    >> 
    >> 
    >> 
    >> >> Dear all,
    >> >>
    >> >> justify argument is hard coded in format.ftable:
    >> >>
    >> >> cbind(apply(LABS, 2L, format, justify = "left"),
    >> >> apply(DATA, 2L, format, justify = "right"))
    >> >>
    >> >> It would be useful to have the possibility to modify the argument between c("left", "right", "centre", "none") as in format.default.
    >> >>
    >> >> The lines could be changed to:
    >> >>
    >> >> if(length(justify) != 2)
    >> >> stop("justify must be length 2")
    >> >> cbind(apply(LABS, 2L, format, justify = justify[1]),
    >> >> apply(DATA, 2L, format, justify = justify[2]))
    >> >>
    >> >> The argument justify could defaults to c("left", "right") for backward compatibility.
    >> >>
    >> >> It could then allow:
    >> >> ftab <- ftable(wool + tension ~ breaks, warpbreaks)
    >> >> format.ftable(ftab, justify = c("none", "none"))
    >> >>
    >> >> Best regards,
    >> >>
    >> >> Thomas


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