An example of regular expressions using capture groups in R.

regex_capture_groups.R

## An example of regular expressions using capture groups
## in R. See:
## http://stackoverflow.com/questions/14700799/r-regex-gsub-extract-part-of-pattern/14714370#14714370
############################################################

# example data
data <-
"Station       lat        lon
1940    K01R    31-08N    092-34W
1941    K01T    28-08N    094-24W
1942    K03Y    48-47N    096-57W
1943    K04V 38-05-50N 106-10-07W
1944    K05F 31-25-16N 097-47-49W
1945    K06D 48-53-04N 099-37-15W"

## read string into a data.frame
df <- read.table(text=data, head=T, stringsAsFactors=F)

## here's the pattern we want to extract
pattern <- "(\\d{1,3})-(\\d{1,3})(?:-(\\d{1,3}))?([NSWE]{1})"

## The stringr library's str_match function returns a data.frame
## in which the first column is the whole matched string and additional
## columns hold the contents of each capture-group in the regex.
library(stringr)
str_match(df$lat, pattern)


## Alternatively, the package gsubfn defines a strapply function,
## which R-ishly applies a function to each matching string.
## True to it's early version number (0.6-5) I came across some
## bugs.
# http://code.google.com/p/gsubfn
# install.packages('gsubfn')
library(gsubfn)
parts <- strapply(df$lat, pattern, FUN=c, simplify=rbind, backref=NULL)

Written in response to a StackOverflow question: R regex / gsub : extract part of pattern