{"id":760,"date":"2015-02-16T12:53:56","date_gmt":"2015-02-16T19:53:56","guid":{"rendered":"http:\/\/homepages.uc.edu\/~yaozo\/wordpress\/?p=760"},"modified":"2015-02-16T12:53:56","modified_gmt":"2015-02-16T19:53:56","slug":"r-regular-expression","status":"publish","type":"post","link":"https:\/\/zhuoyao.net\/index.php\/2015\/02\/16\/r-regular-expression\/","title":{"rendered":"R Regular Expression"},"content":{"rendered":"

R has various functions for regular expression based match and replaces. The grep<\/code>,grepl<\/code>, regexpr<\/code> and gregexpr<\/code> functions are used for searching for matches, while sub<\/code><\/a> andgsub<\/code><\/a> for performing replacement.<\/p>\n

 <\/p>\n

\u2022\u00a0grep(value = FALSE)<\/code> returns an integer vector of the indices of the elements of x<\/code> that yielded a match (or not, for invert = TRUE<\/code>).<\/p>\n

>str <- c(\"Regular\", \"expression\", \"examples of R language\")\n>x <- grep(\"ex\",str,value=F)\n>x\n<\/pre>\n
[1] 2 3<\/p>\n
>x <- \"line 4322: He is now 25 years old, and weights 130lbs\";\n>x <- grep(\"\\\\d\",\"\",x)\n>x\n<\/pre>\n
[1] 1\n<\/pre>\n
 <\/p>\n
\u2022\u00a0grep(value = TRUE)<\/code> returns a character vector containing the selected elements of x<\/code>(after coercion, preserving names but no other attributes).<\/p>\n
>x <- grep(\"ex\",str,value=T)\n>x\n<\/pre>\n
[1] “expression” “examples of R language”<\/p>\n
\u2022\u00a0grepl<\/code> returns a logical vector (match or not for each element of x<\/code>).<\/p>\n
>x <- grepl(\"ex\",str)\n>x\n[1] FALSE  TRUE  TRUE\n<\/pre>\n
 <\/p>\n
\u2022\u00a0sub<\/code> and gsub<\/code> return a character vector of the same length and with the same attributes asx<\/code> (after possible coercion to character). Elements of character vectors x<\/code> which are not substituted will be returned unchanged (including any declared encoding). If useBytes = FALSE<\/code> a non-ASCII substituted result will often be in UTF-8 with a marked encoding (e.g. if there is a UTF-8 input, and in a multibyte locale unless fixed = TRUE<\/code>).<\/p>\n
>str <- c(\"Regular\", \"expression\", \"examples of R language\")\n>x <- sub(\"x.ress\",\"\",str)\n>x\n<\/pre>\n
[1] “Regular” “eion” “examples of R language”<\/p>\n
>x <- sub(\"x.+e\",\"\",str)\n>x\n<\/pre>\n
[1] “Regular” “ession” “e”<\/p>\n
>x <- \"line 4322: He is now 25 years old, and weights 130lbs\";\n>x <- gsub(\"[[:digit:]]\",\"\",x)\n>x\n<\/pre>\n
[1] \"line : He is now  years old, and weights lbs\"\n<\/pre>\n
 <\/p>\n
>x <- \"line 4322: He is now 25 years old, and weights 130lbs\";\n>x <- gsub(\"\\\\d+\",\"\",x)\n>x\n<\/pre>\n
[1] \"line : He is now  years old, and weights lbs\"\n<\/pre>\n
 <\/p>\n
\u2022\u00a0regexpr<\/code> returns an integer vector of the same length as text<\/code> giving the starting position of the first match or -1<\/i> if there is none, with attribute \"match.length\"<\/code>, an integer vector giving the length of the matched text (or -1<\/i> for no match). The match positions and lengths are in characters unless useBytes = TRUE<\/code> is used, when they are in bytes.<\/p>\n
>str <- c(\"Regular\", \"expression\", \"examples of R language\")\n>x <- regexpr(\"x*ress\",str)\n>x\n<\/pre>\n
[1] -1 4 -1<\/p>\n
\u2022\u00a0gregexpr<\/code> returns a list of the same length as text<\/code> each element of which is of the same form as the return value for regexpr<\/code>, except that the starting positions of every (disjoint) match are given.<\/p>\n
>str <- c(\"Regular\", \"expression\", \"examples of R language\")\n>x <- gregexpr(\"x*ress\",str)\n>x\n<\/pre>\n
[[1]]\n[1] -1\nattr(,\"match.length\")\n[1] -1\nattr(,\"useBytes\")\n[1] TRUE\n\n[[2]]\n[1] 4\nattr(,\"match.length\")\n[1] 4\nattr(,\"useBytes\")\n[1] TRUE\n\n[[3]]\n[1] -1\nattr(,\"match.length\")\n[1] -1\nattr(,\"useBytes\")\n[1] TRUE\n<\/pre>\n
 <\/p>\n
Function Syntax:<\/h3>\n
\ngrep(pattern, x, ignore.case = FALSE, perl = FALSE, value = FALSE,\n     fixed = FALSE, useBytes = FALSE, invert = FALSE)\n\ngrepl(pattern, x, ignore.case = FALSE, perl = FALSE,\n      fixed = FALSE, useBytes = FALSE)\n\nsub(pattern, replacement, x, ignore.case = FALSE, perl = FALSE,\n    fixed = FALSE, useBytes = FALSE)\n\ngsub(pattern, replacement, x, ignore.case = FALSE, perl = FALSE,\n     fixed = FALSE, useBytes = FALSE)\n\nregexpr(pattern, text, ignore.case = FALSE, perl = FALSE,\n        fixed = FALSE, useBytes = FALSE)\n\ngregexpr(pattern, text, ignore.case = FALSE, perl = FALSE,\n         fixed = FALSE, useBytes = FALSE)\n\n<\/pre>\n
 <\/p>\n
Regular Expression Syntax:<\/h3>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Syntax<\/td>\nDescription<\/td>\n<\/tr>\n
\\\\d<\/td>\nDigit, 0,1,2 … 9<\/td>\n<\/tr>\n
\\\\D<\/td>\nNot Digit<\/td>\n<\/tr>\n
\\\\s<\/td>\nSpace<\/td>\n<\/tr>\n
\\\\S<\/td>\nNot Space<\/td>\n<\/tr>\n
\\\\w<\/td>\nWord<\/td>\n<\/tr>\n
\\\\W<\/td>\nNot Word<\/td>\n<\/tr>\n
\\\\t<\/td>\nTab<\/td>\n<\/tr>\n
\\\\n<\/td>\nNew line<\/td>\n<\/tr>\n
^<\/td>\nBeginning of the string<\/td>\n<\/tr>\n
$<\/td>\nEnd of the string<\/td>\n<\/tr>\n
\\<\/td>\nEscape special characters, e.g. \\\\ is “\\”, \\+ is “+”<\/td>\n<\/tr>\n
|<\/td>\nAlternation match. e.g. \/(e|d)n\/ matches “en” and “dn”<\/td>\n<\/tr>\n
\u2022<\/td>\nAny character, except \\n or line terminator<\/td>\n<\/tr>\n
[ab]<\/td>\na or b<\/td>\n<\/tr>\n
[^ab]<\/td>\nAny character except a and b<\/td>\n<\/tr>\n
[0-9]<\/td>\nAll Digit<\/td>\n<\/tr>\n
[A-Z]<\/td>\nAll uppercase A to Z letters<\/td>\n<\/tr>\n
[a-z]<\/td>\nAll lowercase a to z letters<\/td>\n<\/tr>\n
[A-z]<\/td>\nAll Uppercase and lowercase a to z letters<\/td>\n<\/tr>\n
i+<\/td>\ni at least one time<\/td>\n<\/tr>\n
i*<\/td>\ni zero or more times<\/td>\n<\/tr>\n
i?<\/td>\ni zero or 1 time<\/td>\n<\/tr>\n
i{n}<\/td>\ni occurs n times in sequence<\/td>\n<\/tr>\n
i{n1,n2}<\/td>\ni occurs n1 – n2 times in sequence<\/td>\n<\/tr>\n
i{n1,n2}?<\/td>\nnon greedy match, see above example<\/td>\n<\/tr>\n
i{n,}<\/td>\ni occures >= n times<\/td>\n<\/tr>\n
[:alnum:]<\/td>\nAlphanumeric characters: [:alpha:] and [:digit:]<\/td>\n<\/tr>\n
[:alpha:]<\/td>\nAlphabetic characters: [:lower:] and [:upper:]<\/td>\n<\/tr>\n
[:blank:]<\/td>\nBlank characters: e.g. space, tab<\/td>\n<\/tr>\n
[:cntrl:]<\/td>\nControl characters<\/td>\n<\/tr>\n
[:digit:]<\/td>\nDigits: 0 1 2 3 4 5 6 7 8 9<\/td>\n<\/tr>\n
[:graph:]<\/td>\nGraphical characters: [:alnum:] and [:punct:]<\/td>\n<\/tr>\n
[:lower:]<\/td>\nLower-case letters in the current locale<\/td>\n<\/tr>\n
[:print:]<\/td>\nPrintable characters: [:alnum:], [:punct:] and space<\/td>\n<\/tr>\n
[:punct:]<\/td>\nPunctuation character: ! ” # $ % & ‘ ( ) * + , – . \/ : ; < = > ? @ [ \\ ] ^ _ ` { | } ~<\/td>\n<\/tr>\n
[:space:]<\/td>\nSpace characters: tab, newline, vertical tab, form feed, carriage return, space<\/td>\n<\/tr>\n
[:upper:]<\/td>\nUpper-case letters in the current locale<\/td>\n<\/tr>\n
[:xdigit:]<\/td>\nHexadecimal digits: 0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
 <\/p>\n","protected":false},"excerpt":{"rendered":"
R has various functions for regular expression based match and replaces. The grep,grepl, regexpr and gregexpr functions are used for searching for matches, while sub… <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[20],"tags":[],"class_list":["post-760","post","type-post","status-publish","format-standard","hentry","category-r"],"_links":{"self":[{"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/posts\/760","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/comments?post=760"}],"version-history":[{"count":0,"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/posts\/760\/revisions"}],"wp:attachment":[{"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/media?parent=760"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/categories?post=760"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zhuoyao.net\/index.php\/wp-json\/wp\/v2\/tags?post=760"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}