regex - Extract a regular expression match

Question

I'm trying to extract a number from a string.

And do something like [0-9]+ on the string "aaa12xxx" and get "12".

I thought it would be something like:

> grep("[0-9]+", "aaa12xxx", value=TRUE)
[1] "aaa12xxx"

And then I figured...

> sub("[0-9]+", "\1", "aaa12xxx")
[1] "aaaxxx"

But I got some form of response doing:

> sub("[0-9]+", "ARGH!", "aaa12xxx")
[1] "aaaARGH!xxx"

There's a small detail I'm missing.

Answer 1

Use the new stringr package which wraps all the existing regular expression operates in a consistent syntax and adds a few that are missing:

library(stringr)
str_locate("aaa12xxx", "[0-9]+")
#      start end
# [1,]     4   5
str_extract("aaa12xxx", "[0-9]+")
# [1] "12"