RE2 is a primarily DFA based regexp engine from Google that is very fast at matching large amounts of text.
From CRAN:
install.packages("re2r")From GitHub:
library(devtools)
install_github("qinwf/re2r", build_vignettes = T)To learn how to use, you can check out the vignettes.
Google Summer of Code - re2 regular expressions.
re2_detect(string, pattern) searches the string expression for a pattern and returns boolean result.
test_string = "this is just one test";
re2_detect(test_string, "(o.e)")## [1] TRUE
Here is an example of email pattern.
show_regex("\\b[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,4}\\b", width = 670, height = 280)
re2_detect("[email protected]", "\\b[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,4}\\b")## [1] TRUE
re2_match(string, pattern) will return the capture groups in ().
(res = re2_match(test_string, "(o.e)"))## .match .1
## [1,] "one" "one"
The return result is a character matrix. .1 is the first capture group and it is unnamed group.
Create named capture group with (?P<name>pattern) syntax.
(res = re2_match(test_string, "(?P<testname>this)( is)"))## .match testname .2
## [1,] "this is" "this" " is"
is.matrix(res)## [1] TRUE
is.character(res)## [1] TRUE
res$testname## testname
## "this"
If there is no capture group, the matched origin strings will be returned.
test_string = c("this is just one test", "the second test");
(res = re2_match(test_string, "is"))## .match
## [1,] "is"
## [2,] NA
re2_match_all() will return the all of patterns in a string instead of just the first one.
res = re2_match_all(c("this is test",
"this is test, and this is not test",
"they are tests"),
pattern = "(?P<testname>this)( is)")
print(res)## [[1]]
## .match testname .2
## [1,] "this is" "this" " is"
##
## [[2]]
## .match testname .2
## [1,] "this is" "this" " is"
## [2,] "this is" "this" " is"
##
## [[3]]
## .match testname .2
is.list(res)## [1] TRUE
match all numbers
texts = c("pi is 3.14529..",
"-15.34 °F",
"128 days",
"1.9e10",
"123,340.00$",
"only texts")
(number_pattern = re2(".*?(?P<number>-?\\d+(,\\d+)*(\\.\\d+(e\\d+)?)?).*?"))## re2 pre-compiled regular expression
##
## pattern: .*?(?P<number>-?\d+(,\d+)*(\.\d+(e\d+)?)?).*?
## number of capturing subpatterns: 4
## capturing names with indices:
## .match number .2 .3 .4
## expression size: 56
(res = re2_match(texts, number_pattern))## .match number .2 .3 .4
## [1,] "pi is 3.14529" "3.14529" NA ".14529" NA
## [2,] "-15.34" "-15.34" NA ".34" NA
## [3,] "128" "128" NA NA NA
## [4,] "1.9e10" "1.9e10" NA ".9e10" "e10"
## [5,] "123,340.00" "123,340.00" ",340" ".00" NA
## [6,] NA NA NA NA NA
res$number## [1] "3.14529" "-15.34" "128" "1.9e10" "123,340.00"
## [6] NA
show_regex(number_pattern)
re2_replace(string, pattern, rewrite)Searches the string "input string" for the occurence(s) of a substring that matches 'pattern' and replaces the found substrings with "rewrite text".
input_string = "this is just one test";
new_string = "my"
re2_replace(new_string, "(o.e)", input_string)## [1] "my"
mask the middle three digits of a US phone number
texts = c("415-555-1234",
"650-555-2345",
"(416)555-3456",
"202 555 4567",
"4035555678",
"1 416 555 9292")
us_phone_pattern = re2("(1?[\\s-]?\\(?\\d{3}\\)?[\\s-]?)(\\d{3})([\\s-]?\\d{4})")
re2_replace(texts, us_phone_pattern, "\\1***\\3")## [1] "415-***-1234" "650-***-2345" "(416)***-3456" "202 *** 4567"
## [5] "403***5678" "1 416 *** 9292"
re2_extract(string, pattern, replacement)Extract matching patterns from a string.
re2_extract("yabba dabba doo", "(.)")## [1] "y"
re2_extract("[email protected]", "(.*)@([^.]*)")## [1] "test@me"
We can create a regular expression object (RE2 object) from a string. It will reduce the time to parse the syntax of the same pattern.
And this will also give us more option for the pattern. run help(re2) to get more detials.
regexp = re2("test",case_sensitive = FALSE)
print(regexp)## re2 pre-compiled regular expression
##
## pattern: test
## number of capturing subpatterns: 0
## capturing names with indices:
## .match
## expression size: 10
regexp = re2("test",case_sensitive = FALSE)
re2_match("TEST", regexp)## .match
## [1,] "TEST"
re2_replace("TEST", regexp, "ops")## [1] "ops"
Use parallel option to enable multithread feature. It will improve performance for large inputs with a multi core CPU.
re2_match(string, pattern, parallel = T)
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