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
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
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tel. + 32 54/436 185
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-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens Titus von der Malsburg
Verzonden: dinsdag 9 juni 2009 11:12
Aan: r-help at 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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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!! > TitusHow 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 -- Ken Knoblauch Inserm U846 Stem-cell and Brain Research Institute Department of Integrative Neurosciences 18 avenue du Doyen L?pine 69500 Bron France tel: +33 (0)4 72 91 34 77 fax: +33 (0)4 72 91 34 61 portable: +33 (0)6 84 10 64 10 http://www.sbri.fr/members/kenneth-knoblauch.html
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: xxxxxxxxxxxxxxxx
Y: yyyyyyyyyyyyyyyy
Extremity splice: xxxxxxxxxxxxxxyyyyyyyyyyyy or
yyyyyyyyyyyyyyxxxxxxxxxx
Middle splice: xxxxxxxyyyyyyyyyyyyyyyxxxxxxxxx or
yyyyyyyxxxxxxxxxxxxxxxyyyyyyyy
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
<malsburg@gmail.com>wrote:
> An operation that I often need is splicing two vectors:
>
> > splice(1:3, 4:6)
> [1] 1 4 2 5 3 6
>
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