re2-package: re2: R interface to the Google's RE2 (C++) regular-expression...

In re2: R Interface to Google RE2 (C++) Regular Expression Library

re2: R interface to the Google's RE2 (C++) regular-expression library

Description

Regular expression matching can be done in two ways: using recursive backtracking or using finite automata-based techniques.

Perl, PCRE, Python, Ruby, Java, and many other languages rely on recursive backtracking for their regular expression implementations. The problem with this approach is that performance can degrade very quickly. Time complexity can be exponential. In contrast, re2 uses finite automata-based techniques for regular expression matching, guaranteeing linear time execution and a fixed stack footprint. See links to Russ Cox's excellent articles in references section.

re2 supports pearl style regular expressions (with extensions like \d, \w, \s, ...) and provides most of the functionality of PCRE – eschewing only backreferences and look-around assertions.

Primary re2 functions

re2 supports three types of operations on a character vector: matching (substring extraction), detection, and replacement.

Matching and substring extraction is provided by re2_match and re2_match_all. Matching regexp "(foo)|(bar)baz" on "barbazbla" will return submatches '.0' = "barbaz", '.1' = NA, and '.2' = "bar". '.0' is the entire matching text. '.1' is the first group, and so on. Groups can also be named.

re2_detect finds the presence of a pattern in a string, like grepl of base R.

re2_replace and re2_replace_all substitute matched substring with replacement string. Replacing first occurrence of pattern "b+" using replacement string "d" on text "yabba dabba doo" will result in "yada dabba doo". Replacing globally will result in "yada dada doo". re2_extract_replace functions like re2_replace except that non-matching text is ignored (not returned).

In all the above functions regexp patterns can be pre-compiled and reused. This greatly improves performance when the same regular-expression pattern is used repeatedly. See re2_regexp.

List of re2 functions :

• re2_match

• re2_match_all

• re2_split

• re2_detect

• re2_which

• re2_subset

• re2_locate

• re2_locate_all

• re2_count

• re2_replace

• re2_replace_all

• re2_extract_replace

• re2_regexp

• re2_get_options

Author(s)

Girish Palya <[e-mail]>

References

• Regular Expression Matching Can Be Simple And Fast https://swtch.com/~rsc/regexp/regexp1.html

• Regular Expression Matching: the Virtual Machine Approach https://swtch.com/~rsc/regexp/regexp2.html

• Regular Expression Matching in the Wild https://swtch.com/~rsc/regexp/regexp3.html

• RE2 Syntax https://github.com/google/re2/wiki/Syntax

• RE2 C++ source https://github.com/google/re2

• R source of RE2 https://github.com/girishji/re2

See Also

Useful links:

• https://github.com/girishji/re2

• Report bugs at https://github.com/girishji/re2/issues

re2 documentation built on March 29, 2022, 5:05 p.m.