On Tue, 4 Apr 2006, Gabor Grothendieck wrote:
> gsubfn in package gsubfn can do this. See the examples
> in ?gsubfn
Thanks. gsubfn looks useful, but may be overkill
for this, and it isn't vectorized. To do what
strsplit(keep=T) would do I think you need to do something like:
> findMatches<-function(strings, pattern){
lapply(strings, function(string){
v <- character()
gsubfn(number.pattern, function(x,...)v<<-c(v,x), string)
v})
}
> number.pattern <-
"[-+]?(([0-9]+(\\.[0-9]*)?)|(\\.[0-9]+))([eE][+-]?[0-9]+)?"
> findMatches(c("12;34:56,89,,12", "1.2, .4, 1., 1e3"), number.pattern)
[[1]]
[1] "12" "34" "56" "89" "12"
[[2]]
[1] "1.2" ".4" "1." "1e3"
Is this worth encapsulating in a standard R function?
If so, is doing via an extra argument to strsplit()
a reasonable way to do it?
> strsplit(c("12;34:56,89,,12", "1.2, .4, 1., 1e3"), number.pattern, keep=T)
[[1]]:
[1] "12" "34" "56" "89" "12"
[[2]]:
[1] "1.2" ".4" "1." "1e3"
> On 4/4/06, Bill Dunlap <[EMAIL PROTECTED]> wrote:
> > strsplit() is a convenient way to get a
> > list of items from a string when you
> > have a regular expression for what is not
> > an item. E.g.,
> >
> > > strsplit("1.2, 34, 1.7e-2", split="[ ,] *")
> > [[1]]:
> > [1] "1.2" "34" "1.7e-2"
> >
> > However, sometimes is it more convenient to
> > give a pattern for the items you do want.
> > E.g., suppose you want to pull all the numbers
> > out of a string which contains a mix of numbers
> > and words. Making a pattern for what a
> > number is simpler than making a pattern
> > for what may come between the number.
> > > number.pattern <-
> > "[-+]?(([0-9]+(\\.[0-9]*)?)|(\\.[0-9]+))([eE][+-]?[0-9]+)?"
> >
> > I propose adding a keep=FALSE argument to
> > strsplit() to do this. If keep is FALSE,
> > then the split argument matches the stuff to
> > omit from the output; if keep is TRUE then
> > split matches the stuff to put into the
> > output. Then we could do the following to
> > get a list of all the numbers in a string
> > (done in a version of strsplit() I'm working on
> > for S-PLUS):
> >
> > > strsplit("1.2, 34, 1.7e-2", split=number.pattern,keep=TRUE)
> > [[1]]:
> > [1] "1.2" "34" "1.7e-2"
> >
> > > strsplit("Ibuprofin 200mg", split=number.pattern,keep=TRUE)
> > [[1]]:
> > [1] "200"
> >
> > Is this a reasonable thing to want strsplit to do?
> > Is this a reasonable parameterization of it?
----------------------------------------------------------------------------
Bill Dunlap
Insightful Corporation
bill at insightful dot com
360-428-8146
"All statements in this message represent the opinions of the author and do
not necessarily reflect Insightful Corporation policy or position."
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