正则表达式用于带有特殊字符的特定模式

Question

I have the following in a data.frame in r:

example <- "Inmuebles24_|.|_Casa_|.|_Renta_|.|_NuevoLeon"

I would like to simply use stringr count and some basic grexpr functions on the string, but i'm stuck on the regex.

The delimiter is clearly (and confusingly): _|.|_

How would this be expressed with regex?

Currently trying to escape everything to no success:

str_count(string = example, pattern = "[\\_\\|\\.\\|\\_]")

Answer 1

Your regex does not work because you placed it into a character class (where you do not need to escape _ , BTW). See my today's answer to Regex expression not working with once or none for an explanation of the issue (mainly, the characters are treated as separate symbols and not as sequences of symbols, and all the special symbols are treated as literals, too).

You can achieve what you want in two steps:

• Trim the string from the delimiters with gsub
• Use str_count + 1 to get the count (as the number of parts = number of delimiters inside the string + 1)

R code:

example <- "_|.|_Inmuebles24_|.|_Casa_|.|_Renta_|.|_NuevoLeon_|.|_"
str_count(string = gsub("^(_[|][.][|]_)+|(_[|][.][|]_)+$", "", example), pattern = "_\\|\\.\\|_") + 1
## => 4

Or, in case you have multile consecutive delimiters, you need another intermediate step to "contract" them into 1:

example <- "_|.|_Inmuebles24_|.|_Casa_|.|__|.|_Renta_|.|__|.|_NuevoLeon_|.|_"
example <- gsub("((_[|][.][|]_)+)", "_|.|_", example)
str_count(string = gsub("^(_[|][.][|]_)+|(_[|][.][|]_)+$", "", example), pattern = "_\\|\\.\\|_") + 1
## => 4

Notes on the regexps: _[|][.][|]_ matches _|.|_ literally as symbols in the [...] character classes lose their special meaning. ((_[|][.][|]_)+) (2) matches 1 or more ( + ) sequences of these delimiters. The ^(_[|][.][|]_)+|(_[|][.][|]_)+$ pattern matches 1 or more delimiters at the start ( ^ ) and end ( $ ) of the string.

Answer 2

这为您提供了本示例的所需内容： str_count(example, "\\\\w+")