R gsub
gsub() function replaces all matches of a string, if the parameter is a string vector, returns a string vector of the same length and with the same attributes
(after possible coercion to character). Elements of string vectors which are not substituted
will be returned unchanged (including any declared encoding).
gsub(pattern, replacement, x, ignore.case = FALSE, perl = FALSE,
fixed = FALSE, useBytes = FALSE)
• pattern: string to be matched, supports regular expression
• replacement: string for replacement
• x: string or string vector
• perl: logical. Should perl-compatible regexps be used? Has priority over extended
• fixed: logical. If TRUE, pattern is a string to be matched as is. Overrides all conflicting arguments
• useBytes: logical. If TRUE the matching is done byte-by-byte rather than character-by-character
> x <- "R Tutorial"
> gsub("ut","ot",x)
[1] "R Totorial"
Case insensitive replace:
> gsub("tut","ot",x,ignore.case=T))
[1] "R otorial"
If ignore.case is not set to True, no replace take place:
> gsub("tut","ot",x)
[1] "R Tutorial"
> x <- "line 4322: He is now 25 years old, and weights 130lbs"
> y <- gsub("\\d+","---",x)
> y
[1] "line ---: He is now --- years old, and weights ---lbs"
> x <- "line 4322: He is now 25 years old, and weights 130lbs"
> y <- gsub("[[:lower:]]","-",x)
> y
[1] "---- 4322: H- -- --- 25 ----- ---, --- ------- 130---"
Vector replacement:
> x <- c("R Tutorial","php Tutorial", "HTML Tutorial")
> gsub("Tutorial","Examples",x)
[1] "R Examples" "php Examples" "HTML Examples"
Other string manipulation functions include sub, regexpr, grep, substr etc.
Regular Expression Syntax:
\
Escape special characters, e.g. \\ is "\", \+ is "+"
|
Alternation match. e.g. /(e|d)n/ matches "en" and "dn"
•
Any character, except \n or line terminator
[^ab]
Any character except a and b
[A-Z]
All uppercase A to Z letters
[a-z]
All lowercase a to z letters
[A-z]
All Uppercase and lowercase a to z letters
i{n}
i occurs n times in sequence
i{n1,n2}
i occurs n1 - n2 times in sequence
i{n1,n2}?
non greedy match, see above example
i{n,}
i occures >= n times
[:alnum:]
Alphanumeric characters: [:alpha:] and [:digit:]
[:alpha:]
Alphabetic characters: [:lower:] and [:upper:]
[:blank:]
Blank characters: e.g. space, tab
[:cntrl:]
Control characters
[:digit:]
Digits: 0 1 2 3 4 5 6 7 8 9
[:graph:]
Graphical characters: [:alnum:] and [:punct:]
[:lower:]
Lower-case letters in the current locale
[:print:]
Printable characters: [:alnum:], [:punct:] and space
[:punct:]
Punctuation character: ! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` { | } ~
[:space:]
Space characters: tab, newline, vertical tab, form feed, carriage return, space
[:upper:]
Upper-case letters in the current locale
[:xdigit:]
Hexadecimal digits: 0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f
