CODEWITHSUNDEEP
regexr
Tyler Rinker
Tyler Rinker

Reputation: 109874

escaping pipe ("|") in a regex

I have a need to split on words and end marks (punctuation of certain types). Oddly pipe ("|") can count as an end mark. I have code that words on end marks until I try to add the pipe. Adding the pipe makes the strsplit every character. Escaping it causes and error. How can I include the pipe int he regular expression?

x <- "I like the dog|."

strsplit(x, "[[:space:]]|(?=[.!?*-])", perl=TRUE)
#[[1]]
#[1] "I"    "like" "the"  "dog|" "."   

strsplit(x, "[[:space:]]|(?=[.!?*-\|])", perl=TRUE)
#Error: '\|' is an unrecognized escape in character string starting "[[:space:]]|(?=[.!?*-\|"

The outcome I'd like:

#[[1]]
#[1] "I"    "like" "the"  "dog"  "|"  "."  #pipe is an element

Upvotes: 17

Views: 38814

Answers (2)

Joshua Ulrich
Joshua Ulrich

Reputation: 176668

One way to solve this is to use the \Q...\E notation to remove the special meaning of any of the characters in .... As it says in ?regex:

If you want to remove the special meaning from a sequence of characters, you can do so by putting them between ‘\Q’ and ‘\E’. This is different from Perl in that ‘$’ and ‘@’ are handled as literals in ‘\Q...\E’ sequences in PCRE, whereas in Perl, ‘$’ and ‘@’ cause variable interpolation.

For example:

> strsplit(x, "[[:space:]]|(?=[\\Q.!?*-|\\E])", perl=TRUE)
[[1]]
[1] "I"    "like" "the"  "dog"  "|"    "."

Upvotes: 19

A5C1D2H2I1M1N2O1R2T1
A5C1D2H2I1M1N2O1R2T1

Reputation: 193547

The problem is actually your hyphen, which should come either first or last:

strsplit(x, "[[:space:]]|(?=[|.!?*-])", perl=TRUE)
strsplit(x, "[[:space:]]|(?=[.|!?*-])", perl=TRUE)
strsplit(x, "[[:space:]]|(?=[.!|?*-])", perl=TRUE)
strsplit(x, "[[:space:]]|(?=[-|.!?*])", perl=TRUE)

and so on should all give you the output you are looking for.

You can also escape the hyphen if you prefer, but remember to use two backslashes!

strsplit(x, "[[:space:]]|(?=[.!?*\\-|])", perl=TRUE)

Upvotes: 12

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