Re: [R] Splicing factors without losing levels
Titus von der Malsburg wrote:
On Tue, Jun 09, 2009 at 11:23:36AM +0200, ONKELINX, Thierry wrote:
For factors, you better convert them first back to character strings.
splice - function(x, y) {
x - levels(x)[x]
y - levels(y)[y]
factor(as.vector(rbind(x, y)))
}
Thank you very much, Thierry!
I failed to mention something important in my last mail: x and y have
the same levels. (I assume that the integer to level name mapping of
a factor defines its class and that it only makes sense to combine
factors of the same class.)
Say
x - factor(c(2,2,4,4), levels=1:4, labels=c(a,b,c,d))
then
x
[1] b b d d
Levels: a b c d
as.integer(x)
[1] 2 2 4 4
but
splice(x,x)
[1] b b b b d d d d
Levels: b d
as.integer(splice(x,x))
[1] 1 1 1 1 2 2 2 2
I'd like to have a splice function that retains the level to label
mapping. One candidate for a solution is:
splice - function(x,y) {
xy - as.vector(rbind(x, y))
if (is.factor(x) is.factor(y))
xy - factor(xy, levels=1:length(levels(x)), labels=levels(x))
xy
}
However, this relies on assumtions about the implementation of
factors that are neither mentioned nor guaranteed in the man page:
Levels are underlyingly integers starting from one and going to
length(levels). levels(x) gives me the labels of these integers in an
order corresponding to 1:length(levels(x)).
Without these assumptions I see no way to recover the integer to level
name mapping for levels that are defined in a factor but do not occur.
I'd be happy if somebody could clarify this issue!
Hm, well,... Some people have been quite insistent that factors should
be though of as isomorphic to vectors over small subsets of character
strings and not as isomorphic to small integers with labels. I tend to
disagree as it creates more complications than it solves.
Anyways, I would do it like this (generalizing 8 and the seq() bits is
left as an exercise)
x - factor(c(2,2,4,4), levels=1:4, labels=c(a,b,c,d))
xx - factor(rep(NA,8),levels=levels(x))
xx[seq(1,8,2)]-x
xx[seq(2,8,2)]-x
xx
[1] b b b b d d d d
Levels: a b c d
as.integer(xx)
[1] 2 2 2 2 4 4 4 4
Titus
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[R] Splicing factors without losing levels
Hi list!
An operation that I often need is splicing two vectors:
splice(1:3, 4:6)
[1] 1 4 2 5 3 6
For numeric vectors I use this hack:
splice - function(x, y) {
xy - cbind(x, y)
xy - t(xy)
dim(xy) - length(x) * 2
return(xy)
}
So far, so good (?). But I also need splicing for factors and I tried
this:
splice - function(x, y) {
xy - cbind(x, y)
xy - t(xy)
dim(xy) - length(x) * 2
if (is.factor(x) is.factor(y)) {
xy - as.factor(xy)
levels(xy) - levels(x)
}
return(xy)
}
This, however, doesn't work because the level name to integer mapping
gets mixed up when copying the levels from x to xy.
My questions:
1.) How can this be fixed?
2.) What's the best way to do splicing of vectors and factors in R?
(I couldn't find a prefdefined function for this although it seems to be
such a basic and useful operation.)
Thanks!!
Titus
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Re: [R] Splicing factors without losing levels
Dear Titus,
Your first function can be simplified to
splice - function(x, y) {
as.vector(rbind(x, y))
}
For factors, you better convert them first back to character strings.
splice - function(x, y) {
x - levels(x)[x]
y - levels(y)[y]
factor(as.vector(rbind(x, y)))
}
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 Titus von der Malsburg
Verzonden: dinsdag 9 juni 2009 11:12
Aan: r-help@r-project.org
Onderwerp: [R] Splicing factors without losing levels
Hi list!
An operation that I often need is splicing two vectors:
splice(1:3, 4:6)
[1] 1 4 2 5 3 6
For numeric vectors I use this hack:
splice - function(x, y) {
xy - cbind(x, y)
xy - t(xy)
dim(xy) - length(x) * 2
return(xy)
}
So far, so good (?). But I also need splicing for factors and I tried
this:
splice - function(x, y) {
xy - cbind(x, y)
xy - t(xy)
dim(xy) - length(x) * 2
if (is.factor(x) is.factor(y)) {
xy - as.factor(xy)
levels(xy) - levels(x)
}
return(xy)
}
This, however, doesn't work because the level name to integer mapping
gets mixed up when copying the levels from x to xy.
My questions:
1.) How can this be fixed?
2.) What's the best way to do splicing of vectors and factors in R?
(I couldn't find a prefdefined function for this although it seems to
be such a basic and useful operation.)
Thanks!!
Titus
__
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Re: [R] Splicing factors without losing levels
Titus von der Malsburg malsburg at gmail.com writes:
An operation that I often need is splicing two vectors:
splice(1:3, 4:6)
[1] 1 4 2 5 3 6
For numeric vectors I use this hack:
splice - function(x, y) {
xy - cbind(x, y)
xy - t(xy)
dim(xy) - length(x) * 2
return(xy)
}
So far, so good (?). But I also need splicing for factors and I tried
this:
splice - function(x, y) {
xy - cbind(x, y)
xy - t(xy)
dim(xy) - length(x) * 2
if (is.factor(x) is.factor(y)) {
xy - as.factor(xy)
levels(xy) - levels(x)
}
return(xy)
}
This, however, doesn't work because the level name to integer mapping
gets mixed up when copying the levels from x to xy.
Thanks!!
Titus
How about something like;:
splice.factor - function(x, y){
if (!(is.factor(x) is.factor(y)))
stop(Both x and y must be factors)
if (length(x) != length(y))
stop(Both x and y must have same length)
lx - levels(x)
ly - levels(y)
lxy - union(lx, ly)
xy - cbind(levels(x)[x], levels(y)[y])
xy - t(xy)
dim(xy) - NULL
xy - factor(xy, levels = lxy)
xy
}
splice.factor(factor(1:3), factor(4:6))
[1] 1 4 2 5 3 6
Levels: 1 2 3 4 5 6
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Re: [R] Splicing factors without losing levels
On Tue, Jun 09, 2009 at 11:23:36AM +0200, ONKELINX, Thierry wrote:
For factors, you better convert them first back to character strings.
splice - function(x, y) {
x - levels(x)[x]
y - levels(y)[y]
factor(as.vector(rbind(x, y)))
}
Thank you very much, Thierry!
I failed to mention something important in my last mail: x and y have
the same levels. (I assume that the integer to level name mapping of
a factor defines its class and that it only makes sense to combine
factors of the same class.)
Say
x - factor(c(2,2,4,4), levels=1:4, labels=c(a,b,c,d))
then
x
[1] b b d d
Levels: a b c d
as.integer(x)
[1] 2 2 4 4
but
splice(x,x)
[1] b b b b d d d d
Levels: b d
as.integer(splice(x,x))
[1] 1 1 1 1 2 2 2 2
I'd like to have a splice function that retains the level to label
mapping. One candidate for a solution is:
splice - function(x,y) {
xy - as.vector(rbind(x, y))
if (is.factor(x) is.factor(y))
xy - factor(xy, levels=1:length(levels(x)), labels=levels(x))
xy
}
However, this relies on assumtions about the implementation of
factors that are neither mentioned nor guaranteed in the man page:
Levels are underlyingly integers starting from one and going to
length(levels). levels(x) gives me the labels of these integers in an
order corresponding to 1:length(levels(x)).
Without these assumptions I see no way to recover the integer to level
name mapping for levels that are defined in a factor but do not occur.
I'd be happy if somebody could clarify this issue!
Titus
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] Splicing factors without losing levels
Various people have provided technical solutions to your problem. May I suggest, though, that 'splice' isn't quite the right word for this operation? Splicing two pieces of rope / movie film / audio tape / wires / etc. means connecting them at their ends, either at an extremity or in the middle, e.g. X: Y: Extremity splice: xx or yyxx Middle splice: xxxyyyx or yyyxxx The splice itself is the point of connection (xy or yx) between two things. In normal English, splicing never refers to interspersing alternate members of X and Y. This may seem like a minor point, but I think it is worthwhile using descriptive names for functions. -s On Tue, Jun 9, 2009 at 5:12 AM, Titus von der Malsburg malsb...@gmail.comwrote: An operation that I often need is splicing two vectors: splice(1:3, 4:6) [1] 1 4 2 5 3 6 [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Splicing factors without losing levels
On Tue, Jun 09, 2009 at 11:04:03AM -0400, Stavros Macrakis wrote: This may seem like a minor point, but I think it is worthwhile using descriptive names for functions. Makes sense. I thought I've seen this use somewhere else (probably in Lisp?). What better name do you suggest for this operation? Titus __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Splicing factors without losing levels
On Tue, Jun 9, 2009 at 11:16 AM, Titus von der Malsburg malsb...@gmail.comwrote: On Tue, Jun 09, 2009 at 11:04:03AM -0400, Stavros Macrakis wrote: This may seem like a minor point, but I think it is worthwhile using descriptive names for functions. Makes sense. I thought I've seen this use somewhere else (probably in Lisp?). What better name do you suggest for this operation? The two meanings I can think of in Lisp for splicing are 1) The backquote operator ,@X, which means to insert the value of X as part of the surrounding list rather than as an element of the list, e.g. `(a b ,@'(c d) e f) == (append '(a b) '(c d) '(e f)) = (a b c d e f), as opposed to `(a b ,'(c d) e f) == (append '(a b) (list '(c d)) '(e f)) = (a b (c d) e f). 2) The notion of inserting (typically destructively) one list in the middle of another. I would suggest a name like 'intersperse' or 'alternate'. -s [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
