POSIX character class does not work in base R regex

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Although stringr ICU regex engines supports bare POSIX character classes in the pattern, in base R regex flavors (both PCRE (perl=TRUE) and TRE), POSIX character classes must be inside bracket expressions. [:alnum:] -> [[:alnum:]].

x <- c("AZaz09 y AZaz09", "ĄŻaz09 y AZŁł09", "26 de Marzo y Pareyra de la Luz")
grepl("[[:alnum:][:blank:]]+[[:blank:]][yY][[:blank:]][[:alnum:][:blank:]]+", x)
## => [1] TRUE TRUE TRUE
grepl("[[:alnum:][:blank:]]+[[:blank:]][yY][[:blank:]][[:alnum:][:blank:]]+", x, perl=TRUE)
## => [1] TRUE TRUE TRUE

See the online demo

When you use [:alnum:] alone, it is a simple bracket expression that matches a single character, a :, a, l, n, u, m.

Pattern details:

  • [[:alnum:][:blank:]]+ – 1+ alphanumeric or horizontal whitespace symbols
  • [[:blank:]] – 1 horizontal whitespace symbols
  • [yY] – either y or Y
  • [[:blank:]] – 1 horizontal whitespace symbols
  • [[:alnum:][:blank:]]+ – 1+ alphanumeric or horizontal whitespace symbols

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