On May 5, 2010, at 5:35 PM, Gabor Grothendieck wrote:
Here are two ways to extract 5 digits.
In the first one \\1 refers to the portion matched between the
parentheses in the regular expression.
In the second one strapply is like apply where the object to be worked
on is the first argument (array for apply, string for strapply) the
second modifies it (which dimension for apply, regular expression for
strapply) and the last is a function which acts on each value
(typically each row or column for apply and each match for strapply).
In this case we use c as our function to just return all the results.
They are returned in a list with one component per string but here
test is just a single string so we get a list one long and we ask for
the contents of the first component using [[1]].
# 1 - sub
sub(".*(\\d{5}).*", "\\1", test)
> test
[1] "</tr><tr><th>88958</th><th>Abcdsef</th><th>67.8S</th><th>68.9\nW</
th><th>26m</th>"
I get different results than I expected given that "\\d" should be
synonymous with "[0-9]":
> sub(".*([0-9]{5}).*", "\\1", test)
[1] "88958"
> sub(".*(\\d{5}).*", "\\1", test)
[1] "</th>"
--
David.
# 2 - strapply - see http://gsubfn.googlecode.com
library(gsubfn)
strapply(test, "\\d{5}", c)[[1]]
On Wed, May 5, 2010 at 5:13 PM, steven mosher
<mosherste...@gmail.com> wrote:
Given a text like
I want to be able to extract a matched regular expression from a
piece of
text.
this apparently works, but is pretty ugly
# some html
test<-"</tr><tr><th>88958</th><th>Abcdsef</th><th>67.8S</
th><th>68.9\nW</th><th>26m</th>"
# a pattern to extract 5 digits
pattern<-"[0-9]{5}"
# regexpr returns a start point[1] and an attribute "match.length"
attr(,"match.length)
# get the substring from the start point to the stop point.. where
stop =
start +length-1
answer<-substr(test,regexpr(pattern,test)[1],regexpr(pattern,test)
[1]+attr(regexpr(pattern,test),"match.length")-1)
answer
[1] "88958"
I tried using sub(pattern, replacement, x ) with a regexp that
captured the
group. I'd found an example of this in the mails
but it didnt seem to work..
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West Hartford, CT
______________________________________________
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and provide commented, minimal, self-contained, reproducible code.
