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

2 messages · Martin Maechler, Gabor Grothendieck

Original
Martin Maechler
# 
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:
'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
[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 at 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


    > -- 
    > Statistics & Software Consulting
    > GKX Group, GKX Associates Inc.
    > tel: 1-877-GKX-GROUP
    > email: ggrothendieck at gmail.com
Gabor Grothendieck
# 
That's not the problem.  The problem is that if you have

   ft <- ftable(UCBAdmissions, row.vars = 3:2)
   ft
   ##             Admit Admitted Rejected
   ## Dept Gender
   ## A    Male              512      313
   ##      Female             89       19
   ## B    Male              353      207
   ##      Female             17        8
   ## C    Male              120      205
  ## ... etc ...

then as.data.frame(ft) gives a deconstructed 24x4 data.frame
like this:

  as.data.frame(ft)
  ##    Dept Gender    Admit Freq
  ## 1     A   Male Admitted  512
  ## 2     B   Male Admitted  353
  ## 3     C   Male Admitted  120
  ## 4     D   Male Admitted  138
  ## ... etc ...

which is fine but it does not address the problem here.  The
problem here is that we want a a usable data.frame
having columns that correspond to ft.  We want this 12x4
data.frame:

  ##    Dept Gender Admitted Rejected
  ## 1     A   Male      512      313
  ## 2     A Female       89       19
  ## 3     B   Male      353      207
  ## 4     B Female       17        8
  ## ... etc ...

The links I provided already pointed to the code below which
someone posted on SO and solves the problem but I would
have thought this would be easy to do in base R and natural
to provide.

  ftable2df <- function(mydata) {
    ifelse(class(mydata) == "ftable",
        mydata <- mydata, mydata <- ftable(mydata))
    dfrows <- rev(expand.grid(rev(attr(mydata, "row.vars"))))
    dfcols <- as.data.frame.matrix(mydata)
    names(dfcols) <- do.call(
      paste, c(rev(expand.grid(rev(attr(mydata, "col.vars")))), sep = "_"))
    cbind(dfrows, dfcols)
  }
  ftable2df(ft)
  ##    Dept Gender Admitted Rejected
  ## 1     A   Male      512      313
  ## 2     A Female       89       19
  ## 3     B   Male      353      207
  ## 4     B Female       17        8
  ## ... etc ...

 Fri, May 15, 2020 at 12:25 PM Martin Maechler
<maechler at stat.math.ethz.ch> wrote: