Using group and backreference in regex in R - stringr::str_replace

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I have a simple situation, but I'm struggling to use group and backreference in regex. How could I do that with stringr::str_replace ?.

For example, I want to transform test.txt in test.evaluation.txt. I'm wishing something like this:

stringr::str_replace("test.txt", "\\.(\\1)$", ".evaluation.(\\1)")

I'd like to use the group "1" to save the file format. Thanks in advance if someone can help with an answer in this format.

EDIT With stringr:

stringr::str_replace_all(my_string,"([a-z])(.txt)","\\1.evaluation\\2")
[1] "test.evaluation.txt"

Not the most efficient:

my_string<-"test.txt"
res<-unlist(strsplit(my_string,"\\."))
paste0(res[1],".evaluation.",res[2])
[1] "test.evaluation.txt"

Replace matched patterns in a string — str_replace • stringr, Source: R/replace.r str_replace(string, pattern, replacement) str_replace_all( string, pattern, is a regular expression, as described in stringi::stringi-search- regex. be replaced with the contents of the respective matched group (created by () ). To replace the complete string with NA , use replacement = NA_character_ . The default interpretation is a regular expression, as described in stringi::stringi-search-regex. Control options with regex(). Match a fixed string (i.e. by comparing only bytes), using fixed(). This is fast, but approximate. Generally, for matching human text, you'll want coll() which respects character matching rules for the specified locale.

An option with sub to match a . and replace it with . followed by 'evaluation' and another .

sub("\\.", ".evaluation.", my_string)
#[1] "test.evaluation.txt"

Regular expressions • stringr, And this tells R to look for an explicit . str_extract(c("abc", "a.c", "bef"), "a\\.c") To create that regular expression, you need to use a string, which also needs to escape \ . "_") #> [1] "_The_ _quick_ _brown_ _fox_" str_replace_all("The quick brown Parenthesis also define “groups” that you can refer to with backreferences,� Capturing group \(regex\) Escaped parentheses group the regex between them. They capture the text matched by the regex inside them into a numbered group that can be reused with a numbered backreference. They allow you to apply regex operators to the entire grouped regex. \(abc \) {3} matches abcabcabc. First group matches abc. no: no: no: no

With capturing groups:

sub("\\.([[:alnum:]]+)$","\\.evaluation\\.\\1","text.txt")
[1] "text.evaluation.txt"

Regular Expressions in R, Regular expression is a pattern that describes a specific set of strings with a common structure. Replace a pattern: gsub() , stringr::str_replace() , stringr:: str_replace_all() Each group can than be refer using \\N , with N being the No. of (. letter i or t , and ends with land , and replace land with LAND using backreference. sub & gsub R Functions; R Functions List (+ Examples) The R Programming Language . In this R programming tutorial you learned how to change matched patterns in strings. Let me know in the comments section below, in case you have additional questions or comments.

14 Strings, I recommend always using " , unless you want to create a string that contains If you want them to print as "NA" , use str_replace_na() : Given the corpus of common words in stringr::words , create regular expressions that find all words that: as previously matched by a capturing group with backreferences, like \1 , \ 2 etc. When there are fewer capturing groups than the 2-digit number, treat this as a single-digit backreference followed by a literal number instead of as an invalid backreference. Replacing ( a ) ( b ) ( c ) with $3 9 $3 8 $1 7 in abc yields c9c8a7

Regular expressions, And this tells R to look for an explicit . str_extract(c("abc", "a.c", "bef"), "a\\.c") To create that regular expression, you need to use a string, which also needs to escape \ . "_") #> [1] "_The_ _quick_ _brown_ _fox_" str_replace_all("The quick brown Parenthesis also define “groups” that you can refer to with backreferences,� Backreferences to Non-Existent Capturing Groups. An invalid backreference is a reference to a number greater than the number of capturing groups in the regex or a reference to a name that does not exist in the regex. Such a backreference can be treated in three different ways. Delphi, Perl, Ruby, PHP, R, Boost, std::regex, XPath, and Tcl

[PDF] Regular Expressions, extract all matches + individual character groups stringr::str_replace_all(string, pattern, replacement) By default R uses POSIX extended regular using (?i). In backreferences, the strings can be converted to lower or upper case using \\L� Parenthesis also define “groups” that you can refer to with backreferences, like \1, \2 etc, and can be extracted with str_match(). For example, the following regular expression finds all fruits that have a repeated pair of letters:

Comments
  • I think the pattern match should be differnt
  • stringr::str_replace("test.txt", "\\.([^.]*)$", ".evaluation.\\1")