R之字符串相关

最新推荐文章于 2023-08-01 14:03:40 发布

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本文详细介绍了R语言中用于字符串操作的几个关键函数，包括strsplit、substr等，并通过示例展示了如何使用这些函数进行字符串分割、截取与连接。此外，还介绍了字符串替换、大小写转换、字符匹配等功能，提供了实用的编程技巧。

1.strsplit(m,n) 分割字符串:将字符串m,在含有字符n的地方进行分割

如：strsplit("abcdef","e"):

结果为：

[[1]]
[1] "abcd" "f"

strsplit(c("ab","cde","mnd"),"e") 结果为：

[[1]]
[1] "ab"

[[2]]
[1] "cd"

[[3]]
[1] "mnd"

2.substr(m,index1,length):截取字符串m,从index1索引处截取长度为length的字符串；

> substr("abcde",1,3)
[1] "abc"

#字符串连接：
paste() #paste(..., sep = " ", collapse = NULL)

#字符串分割：
strsplit() #strsplit(x, split, extended = TRUE, fixed = FALSE, perl = FALSE)

#计算字符串的字符数：
nchar()

#字符串截取：
substr(x, start, stop)
substring(text, first, last = 1000000)
substr(x, start, stop) <- value
substring(text, first, last = 1000000) <- value

#字符串替换及大小写转换：
chartr(old, new, x)
tolower(x)
toupper(x)
casefold(x, upper = FALSE)

字符完全匹配
grep()
字符不完全匹配
agrep()
字符替换
gsub()
#以上这些函数均可以通过perl=TRUE来使用正则表达式。
     grep(pattern, x, ignore.case = FALSE, extended = TRUE,
          perl = FALSE, value = FALSE, fixed = FALSE, useBytes = FALSE)

     sub(pattern, replacement, x,
         ignore.case = FALSE, extended = TRUE, perl = FALSE,
         fixed = FALSE, useBytes = FALSE)

     gsub(pattern, replacement, x,
          ignore.case = FALSE, extended = TRUE, perl = FALSE,
          fixed = FALSE, useBytes = FALSE)

     regexpr(pattern, text, ignore.case = FALSE, extended = TRUE,
             perl = FALSE, fixed = FALSE, useBytes = FALSE)

     gregexpr(pattern, text, ignore.case = FALSE, extended = TRUE,
              perl = FALSE, fixed = FALSE, useBytes = FALSE)
See Also:

     regular expression (aka 'regexp') for the details of the pattern
     specification.

     'glob2rx' to turn wildcard matches into regular expressions.

     'agrep' for approximate matching.

     'tolower', 'toupper' and 'chartr' for character translations.
     'charmatch', 'pmatch', 'match'. 'apropos' uses regexps and has
     nice examples.