Dear Baptiste,
You can avoid the recursive stuff. And it will run about twice as
fast.
order.factor <- function (x, ref)
+ {
+ last.index <- length(ref) # convenience for matlab's end keyword
+ if(last.index == 1) return(relevel(x, ref)) # end case, normal case
+ my.new.list <- list(x=relevel(x, ref[last.index]), ref=ref[-
last.index])
+ return(do.call(order.factor, my.new.list)) # recursive call
+ }
order.factor2 <- function(x, ref){
+ factor(x, levels = c(ref, sort(levels(x)[!levels(x) %in% ref])))
+ }
order.factor3 <- function(x, ref){
+ factor(x, levels = c(ref, sort(levels(x)[!levels(x) %in%
ref])), labels = c(ref, sort(levels(x)[!levels(x) %in% ref])))
+ }
x <- factor(sample(LETTERS[1:5], 10000000, replace = TRUE))
y <- factor(sample(LETTERS[1:20], 10000000, replace = TRUE))
system.time(order.factor(x, c("D", "B")))
user system elapsed
5.69 0.38 6.09
system.time(order.factor2(x, c("D", "B")))
user system elapsed
3.90 0.20 4.12
system.time(order.factor3(x, c("D", "B")))
user system elapsed
3.26 0.19 3.46
system.time(order.factor(y, c("D", "B")))
user system elapsed
17.43 0.39 17.84
system.time(order.factor3(y, c("D", "B")))
user system elapsed
8.25 0.17 8.46
HTH,
Thierry
----------------------------------------------------------------------------
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for
Nature and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
thierry.onkel...@inbo.be
www.inbo.be
To call in the statistician after the experiment is done may be no
more than asking him to perform a post-mortem examination: he may be
able to say what the experiment died of.
~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data.
~ Roger Brinner
The combination of some data and an aching desire for an answer does
not ensure that a reasonable answer can be extracted from a given
body of data.
~ John Tukey
-----Oorspronkelijk bericht-----
Van: r-help-boun...@r-project.org [mailto:r-help-boun...@r-
project.org] Namens baptiste auguie
Verzonden: vrijdag 9 januari 2009 15:11
Aan: R R-help
Onderwerp: [R] recursive relevel
Dear list,
I'm having second thoughts after solving a very trivial problem: I
want to extend the relevel() function to reorder an arbitrary number
of levels of a factor in one go. I could not find a trivial way of
using the code obtained by getS3method("relevel","factor"). Instead, I
thought of solving the problem in a recursive manner (possibly after
reading Paul Graham essays on Lisp too recently). Here is my attempt :
order.factor <- function (x, ref)
{
last.index <- length(ref) # convenience for matlab's end keyword
if(last.index == 1) return(relevel(x, ref)) # end case, normal
case
of relevel
my.new.list <- list(x=relevel(x, ref[last.index]), # creating a
list with updated parameters,
# going
through the list in reverse order
ref=ref[-
last.index]) # chop the vector from its last level
return(do.call(order.factor, my.new.list)) # recursive call
}
ff <- factor(c("a", "b", "c", "d"))
ff
relevel(ff, levels(ff)[1])
relevel(ff, levels(ff)[2]) # that's the usual case: you want to put
a level first
order.factor(x=ff, ref=c("a", "b"))
order.factor(x=ff, ref=c("c"))
order.factor(x=ff, ref=c("c", "d")) # that's my wish: put c and d in
that order as the first two levels
I'm hoping this can be improved in several aspects:
- there is probably already a better function I missed or overlooked
(I'd still be curious about the following points, though)
- after reading a few threads, it appears that some recursive
functions are fragile in some sense, and I'm not sure what this means
in practice. (Should I use Recall, somehow?)
- it's probably quite slow for large data.frames
- I could not think of a good name, this one might clash with some S3
method perhaps?
- any other thoughts welcome!
Best wishes,
Baptiste
_____________________________
Baptiste Auguié
School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK
Phone: +44 1392 264187
http://newton.ex.ac.uk/research/emag
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