Extract numbers between brackets within a string [duplicate]

Answer 1

Here is a gsubfn solution:

library(gsubfn)

strapplyc(x, "[(](\\d+)[)]", simplify = TRUE)

[(] matches an open paren, (\\d+) matches a string of digits creating a back-reference owing to the parens around it and finally [)] matches a close paren. The back-reference is returned.

Answer 2

There are many possible regular expressions to do this. Here is one:

x=c("East Kootenay C (5901035) RDA 01011","Thompson-Nicola J (Copper Desert Country) (5933039) RDA 02020")

> gsub('.+\\(([0-9]+)\\).+?$', '\\1', x)
[1] "5901035" "5933039"

Lets break down the syntax of that first expression '.+\\(([0-9]+)\\).+'

• .+ one or more of anything

• \\( parentheses are special characters in a regular expression, so if I want to represent the actual thing ( I need to escape it with a \. I have to escape it again for R (hence the two \s).

• ([0-9]+) I mentioned special characters, here I use two. the first is the parentheses which indicate a group I want to keep. The second [ and ] surround groups of things. see ?regex for more information.

• ?$ The final piece assures that I am grabbing the LAST set of numbers in parens as noted in the comments.

I could also use * instead of . which would mean 0 or more rather than one or more i in case your paren string comes at the beginning or end of a string.

The second piece of the gsub is what I am replacing the first portion with. I used: \\1. This says use group 1 (the stuff inside the ( ) from above. I need to escape it twice again, once for the regex and once for R.

Clear as mud to be sure! Enjoy your data munging project!