R語言gsub替換字元工具的具體使用

2021-03-11 10:00:25

gsub()可以用於欄位的刪減、增補、替換和切割，可以處理一個欄位也可以處理由欄位組成的向量。

具體的使用方法為：gsub("目標字元", "替換字元", 物件)

在gsub函數中，任何欄位處理都由將「替換字元」替換到「目標字元」這一流程中實現，令替換字元為''''可實現刪除，令替換字元為"目標字元+增補內容"可實現增補，替換和切割也是使用類似的操作。

> text <- "AbcdEfgh . Ijkl MNM"
> gsub("Efg", "AAA", text) #將Efg改為AAA，區分大小寫
[1] "AbcdAAAh . Ijkl MNM"

任何符號，包括空格、Tab和換行都是可以識別的

> gsub(" I", "i", text)  #可識別空格
[1] "AbcdEfgh .ijkl MNM"

同時字元可以識別多個，進行批次置換

> gsub("M", "N", text) 
[1] "AbcdEfgh . Ijkl NNN"

除此之外，gsub還有其他批次操作的方法

> gsub("^.* ", "a", text) #開頭直到最後一個空格結束替換成a
[1] "aMNM"
> gsub("^.* I(j).*$", "1", text) #只保留一個j
[1] "j"
> gsub(" .*$", "b", text) #第一個空格直達結尾替換成b
[1] "AbcdEfghb"
> gsub(".", "+", text) #句號.和加號+是特殊的，要新增來識別
[1] "AbcdEfgh + Ijkl MNM"

Syntax	Description
d	Digit, 0,1,2 ... 9
D	Not Digit
s	Space
S	Not Space
w	Word
W	Not Word
t	Tab
n	New line
^	Beginning of the string
$	End of the string
	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]	a or b
[^ab]	Any character except a and b
[0-9]	All Digit
[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+	i at least one time
i*	i zero or more times
i?	i zero or 1 time
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

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R語言gsub替換字元工具的具體使用

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