I unintentionally missed to cc to r-devel.
-------- Original Message --------
Subject: Re: [Rd] levels for list and data.frame
Date: Tue, 21 Mar 2006 20:50:21 +0100
From: Gregor Gorjanc <[EMAIL PROTECTED]>
Reply-To: [EMAIL PROTECTED]
To: Martin Maechler <[EMAIL PROTECTED]>
References: <[EMAIL PROTECTED]>
<[EMAIL PROTECTED]>
Martin Maechler wrote:
> Hi Gregor,
>
> before even considering methods for "list" and "data.frame",
> can you explain why you think it is important for levels() to
> become a generic function at all?
> For me, levels belong to factors (or then to contour plots, or
> co-plots ) but exactly because level is a too generic word, it
> seems to me to be problematic as a generic function.
>
> How would describe the purpose of the levels() generic?
>
You are right. I was in situation where I wanted to get levels from all
entries (factors) of a list and considered to write a method for this
instead of always using lapply(). It went quite smoothly, if I skip R
CMD check error. After that I began to think and post a question to
R-devel. Perhaps levels is really to generic, however one can set levels
also for non-factors. Although, I agree that this is of no use. I was
also playing with levels<- and find it quite hard to do something
general and usable for lists and data.frame.
If we put levels aside, is there any opinion/policy about list,
data.frame methods? Just curiosity.
>
>>>>>>"Gregor" == Gregor Gorjanc <[EMAIL PROTECTED]>
>>>>>> on Mon, 20 Mar 2006 23:27:21 +0100 writes:
>
>
> Gregor> oops, this does not pass R CMD check. I will have to read manuals
> a bit
> Gregor> more.
>
> Gregor> ...
> Gregor> * checking S3 generic/method consistency ... WARNING
> Gregor> levels:
> Gregor> function(x, ...)
> Gregor> levels.list:
> Gregor> function(x, drop)
>
> Gregor> levels:
> Gregor> function(x, ...)
> Gregor> levels.data.frame:
> Gregor> function(x, drop)
> Gregor> ...
>
> Gregor> Anyway, I would like to ask what is the "opinion" about writing
> methods
> Gregor> for classes as list and data.frame. Methods for this might not be
> as
> Gregor> simple as for numeric, character, factor and it would be nice
> that there
> Gregor> would be some guidelines for at least:
> Gregor> - what should be the "general" output i.e. list or something else
> - I
> Gregor> understand that it is hard to say in advance, but a common policy
> might
> Gregor> not hurt
> Gregor> - what to do if a method for a list or data.frame can not be
> applied to
> Gregor> each entry/column
>
>
> >> Hello!
> >>
> >> Does R core find the following pacth usefull - I created methods for
> >> levels for list and data.frame, which can be usefull to get a list of
> >> levels for entries in a list or columns in a data.frame. Patch is
> >> attached and shown bellow example
> >>
> >> # Example
> >>> tmp <- list()
> >>> tmp$a <- factor(letters[1:10])
> >>> tmp$b <- factor(letters[5:14])
> >>> tmp$c <- 1:10
> >>> tmp1 <- as.data.frame(tmp)
> >>> tmp2 <- list()
> >>> tmp2$"1" <- tmp
> >>> tmp2$"2" <- tmp1
> >>> str(tmp2)
> >> List of 2
> >> $ 1:List of 3
> >> ..$ a: Factor w/ 10 levels "a","b","c","d",..: 1 2 3 4 5 6 7 8 9 10
> >> ..$ b: Factor w/ 10 levels "e","f","g","h",..: 1 2 3 4 5 6 7 8 9 10
> >> ..$ c: int [1:10] 1 2 3 4 5 6 7 8 9 10
> >> $ 2:`data.frame': 10 obs. of 3 variables:
> >> ..$ a: Factor w/ 10 levels "a","b","c","d",..: 1 2 3 4 5 6 7 8 9 10
> >> ..$ b: Factor w/ 10 levels "e","f","g","h",..: 1 2 3 4 5 6 7 8 9 10
> >> ..$ c: int [1:10] 1 2 3 4 5 6 7 8 9 10
> >>
> >>> levels(tmp2)
> >> $"1"
> >> $"1"$a
> >> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
> >>
> >> $"1"$b
> >> [1] "e" "f" "g" "h" "i" "j" "k" "l" "m" "n"
> >>
> >>
> >> $"2"
> >> $"2"$a
> >> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
> >>
> >> $"2"$b
> >> [1] "e" "f" "g" "h" "i" "j" "k" "l" "m" "n"
> >>
> >>> levels(tmp2, drop = FALSE)
> >> $"1"
> >> $"1"$a
> >> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
> >>
> >> $"1"$b
> >> [1] "e" "f" "g" "h" "i" "j" "k" "l" "m" "n"
> >>
> >> $"1"$c
> >> NULL
> >>
> >>
> >> $"2"
> >> $"2"$a
> >> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
> >>
> >> $"2"$b
> >> [1] "e" "f" "g" "h" "i" "j" "k" "l" "m" "n"
> >>
> >> $"2"$c
> >> NULL
> >>
> >> ----------------------------------------------------------------------
> >>
> >> $ svn diff factor.R
> >> Index: factor.R
> >> ===================================================================
> >> --- factor.R (revision 37559)
> >> +++ factor.R (working copy)
> >> @@ -25,7 +25,25 @@
> >> ## Help old S users:
> >> category <- function(...) .Defunct()
> >>
> >> -levels <- function(x) attr(x, "levels")
> >> +levels <- function(x, ...) UseMethod("levels")
> >> +
> >> +levels.default <- function(x, ...) attr(x, "levels")
> >> +
> >> +levels.list <- function(x, drop = TRUE)
> >> +{
> >> + tmp <- lapply(x, levels, drop = drop)
> >> + if (drop) {
> >> + tmp1 <- unlist(lapply(tmp, is.null))
> >> + tmp <- tmp[!tmp1]
> >> + }
> >> + return(tmp)
> >> +}
> >> +
> >> +levels.data.frame <- function(x, ...)
> >> +{
> >> + return(levels.list(x, ...))
> >> +}
> >> +
> >> nlevels <- function(x) length(levels(x))
> >>
> >> "levels<-" <- function(x, value) UseMethod("levels<-")
> >>
>
> Gregor> --
> Gregor> Lep pozdrav / With regards,
> Gregor> Gregor Gorjanc
>
> Gregor>
> ----------------------------------------------------------------------
> Gregor> University of Ljubljana PhD student
> Gregor> Biotechnical Faculty
> Gregor> Zootechnical Department URI:
> http://www.bfro.uni-lj.si/MR/ggorjan
> Gregor> Groblje 3 mail: gregor.gorjanc <at>
> bfro.uni-lj.si
>
> Gregor> SI-1230 Domzale tel: +386 (0)1 72 17 861
> Gregor> Slovenia, Europe fax: +386 (0)1 72 17 888
>
> Gregor>
> ----------------------------------------------------------------------
> Gregor> "One must learn by doing the thing; for though you think you know
> it,
> Gregor> you have no certainty until you try." Sophocles ~ 450 B.C.
>
> Gregor> ______________________________________________
> Gregor> R-devel@r-project.org mailing list
> Gregor> https://stat.ethz.ch/mailman/listinfo/r-devel
>
--
Lep pozdrav / With regards,
Gregor Gorjanc
----------------------------------------------------------------------
University of Ljubljana PhD student
Biotechnical Faculty
Zootechnical Department URI: http://www.bfro.uni-lj.si/MR/ggorjan
Groblje 3 mail: gregor.gorjanc <at> bfro.uni-lj.si
SI-1230 Domzale tel: +386 (0)1 72 17 861
Slovenia, Europe fax: +386 (0)1 72 17 888
----------------------------------------------------------------------
"One must learn by doing the thing; for though you think you know it,
you have no certainty until you try." Sophocles ~ 450 B.C.
----------------------------------------------------------------------
--
Lep pozdrav / With regards,
Gregor Gorjanc
----------------------------------------------------------------------
University of Ljubljana PhD student
Biotechnical Faculty
Zootechnical Department URI: http://www.bfro.uni-lj.si/MR/ggorjan
Groblje 3 mail: gregor.gorjanc <at> bfro.uni-lj.si
SI-1230 Domzale tel: +386 (0)1 72 17 861
Slovenia, Europe fax: +386 (0)1 72 17 888
----------------------------------------------------------------------
"One must learn by doing the thing; for though you think you know it,
you have no certainty until you try." Sophocles ~ 450 B.C.
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