6.12 Regexp Character Classes

20180608 A character class is a collection of characters that are in some way grouped together. We enclose the characters to be grouped within square backets []. The pattern then matches any one of the characters in the set. For example, the character class [0-9] matches any of the digits from 0 to 9.

% latex table generated in R 4.1.0 by xtable 1.8-4 package % Sat Jun 5 10:45:08 2021
s <- c("abc12", "@#$", "345", "ABcd")
grep(pattern="[0-9]+", s, value=TRUE)
## [1] "abc12" "345"
grep(pattern="[A-Z]+", s, value=TRUE)
## [1] "ABcd"
grep(pattern="[^@#$]+", s, value=TRUE)
## [1] "abc12" "345"   "ABcd"

R also supports the use of POSIX character classes which are represented within [[]] (double braces).

grep(pattern="[[:alpha:]]", s, value=TRUE)
## [1] "abc12" "ABcd"
grep(pattern="[[:upper:]]", s, value=TRUE)
## [1] "ABcd"

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