POSIX character class does not work in base R regex

Question

I\'m having some problems matching a pattern with a string of text in R.

I\'m trying to get TRUE with grepl when the text is s

Answer 1

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