How to use regex character class extensions in R?

Question

This simple regular expression for matching each single digit

gregexpr('[[:digit:]]', 'a1b2c3')

returns what I expect:

[[1]]
[1] 2 4 6
attr(,"match.length")
[1] 1 1 1
attr(,"useBytes")
[1] TRUE

But the R documentation suggests a more compact syntax:

Symbols \d, \s, \D and \S denote the digit and space classes and their negations (these are all extensions).

So I tried

gregexpr('[\d]', 'a1b2c3')

but this returns an error:

Error: '\d' is an unrecognized escape in character string starting "'[\d"

How is this "extension" used?

Answer 1

The equivalent of

gregexpr('[[:digit:]]', 'a1b2c3')

is

gregexpr('\\d', 'a1b2c3')

You need to precede the regex character class by a double backslash (\\).