gsub(pattern, replacement, x, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE)grep(pattern, x, ignore.case = FALSE, perl = FALSE, value = FALSE, fixed = FALSE, useBytes = FALSE, invert = FALSE)grepl(pattern, x, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE) sub(pattern, replacement, x, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE)regexpr(pattern, text, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE)gregexpr(pattern, text, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE) regexec(pattern, text, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE)各常用功能介绍：
gsub()：对查找到的所有内容进行替换，返回替换后的text；否则直接返回text
sub()：只对查找到的第一个内容进行替换
注意：sub()是对字符串中查找到的第一个进行替换，x可以是一个向量，举例如下：
a <- c(12,123,234)
x <- c(a,a,a)
sub("2","r",a)
sub("2","r",x)
gsub("2","r",a)
gsub("2","r",x)可以跑一下代码感受下
grep()：查找，存在参数value，返回结果是匹配项的下标
grep1()：查找，返回值为true
pattern：替换什么（即正则表达式：被用来检索、替换那些符合某个模式/规则的文本）
replacement：替换成什么
x：在哪里/什么里面替换
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ignore.case：FALSE表示区分大小写；TRUE则忽略大小写
perl：是否使用perl兼容的正则表达式（regexps）（TRUE/FALSE）
fixed：如果为TRUE，pattern是要匹配的字符串。覆盖所有冲突的参数
useBytes：默认为false，当为true时，则是逐字节逐字节匹配而不是逐字符逐字符匹配。
- gsub()与sub()区别
sub()只对查找到的第一个内容进行替换；gsub()对查找到的所有内容进行替换
| 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 |