R: How to extract specific digits from a string?

Question

I want to retrieve the first Numbers (here -> 344002) from a string:

string <- '<a href="/Archiv-Suche/!344002&amp;s=&amp;SuchRahmen=Print/" ratiourl-ressource="344002"'

I am preferably looking for a regular expression, which looks for the Numbers after the ! and before the &amp.

All I came up with is this but this catches the ! as well (!344002):

regmatches(string, gregexpr("\\!([[:digit:]]+)", string, perl =TRUE))

Any ideas?

`sub('.*?!(\\d+)&.*', '\\1', string)` – alistaire Nov 14 '16 at 00:37 — alistaire, Nov 14 '16 at 00:37

score 2 · Accepted Answer · answered Nov 14 '16 at 00:55

2

Use this regex:

(?<=\!)\d+(?=&amp)

Use this code:

regmatches(string, gregexpr("(?<=\!)\d+(?=&amp)", string, perl=TRUE))

(?<=\!) is a lookbehind, the match will start following !
\d+ matches one digit or more
(?=&amp) stops the match if next characters are &amp

answered Nov 14 '16 at 00:55

Nicolas

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You need to double escape like \\d+ and I don't think you need to escape the ! at all `regmatches(string, gregexpr("(?<=!)\\d+(?=&amp)", string, perl=TRUE))` for instance. But +1. – thelatemail Nov 14 '16 at 01:44
Thank you for the quick help! – Nov 14 '16 at 10:39

score 0 · Answer 2 · edited May 23 '17 at 12:24

0

library(gsubfn)
strapplyc(string, "!(\\d+)")[[1]]

Old answer]

Test this code.

library(stringr)
str_extract(string, "[0-9]+")

similar question&answer is present here

Extract a regular expression match in R version 2.10

edited May 23 '17 at 12:24

Community

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answered Nov 14 '16 at 00:38

JKim

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this doesnt guarantee you get the digits after the ! and before the & – rawr Nov 14 '16 at 00:48

score 0 · Answer 3 · answered Nov 14 '16 at 01:05

You may capture the digits (\d+) in between ! and &amp and get it with regexec/regmatches:

> string <- '<a href="/Archiv-Suche/!344002&amp;s=&amp;SuchRahmen=Print/" ratiourl-ressource="344002"'
> pattern = "!(\\d+)&amp;"
> res <- unlist(regmatches(string,regexec(pattern,string)))
> res[2]
[1] "344002"

See the online R demo

R: How to extract specific digits from a string?

3 Answers3