library(stringr)1. stringr包函数一览
1.1 字符串拼接函数
- str_c: 字符串拼接。
- str_join: 字符串拼接，同str_c。
- str_trim: 去掉字符串的空格和TAB()
- str_pad: 补充字符串的长度
- str_dup: 复制字符串
- str_wrap: 控制字符串输出格式
- str_sub: 截取字符串
- str_sub<- 截取字符串，并赋值，同str_sub
1.2 字符串计算函数
- str_count: 字符串计数
- str_length: 字符串长度
- str_sort: 字符串值排序
- str_order: 字符串索引排序，规则同str_sort
1.3 字符串匹配函数
- str_split: 字符串分割
- str_split_fixed: 字符串分割，同str_split
- str_subset: 返回匹配的字符串
- word: 从文本中提取单词
- str_detect: 检查匹配字符串的字符
- str_match: 从字符串中提取匹配组。
- str_match_all: 从字符串中提取匹配组，同str_match
- str_replace: 字符串替换
- str_replace_all: 字符串替换，同str_replace
- str_replace_na:把NA替换为NA字符串
- str_locate: 找到匹配的字符串的位置。
- str_locate_all: 找到匹配的字符串的位置,同str_locate
- str_extract: 从字符串中提取匹配字符
- str_extract_all: 从字符串中提取匹配字符，同str_extract
1.4 字符串变换函数
- str_conv: 字符编码转换
- str_to_upper: 字符串转成大写
- str_to_lower: 字符串转成小写,规则同str_to_upper
- str_to_title: 字符串转成首字母大写,规则同str_to_upper
1.5 参数控制函数，仅用于构造功能的参数，不能独立使用。
- boundary: 定义使用边界
- coll: 定义字符串标准排序规则。
- fixed: 定义用于匹配的字符，包括正则表达式中的转义符
- regex: 定义正则表达式
2. 详细函数
2.1 字符串拼接函数
2.1.1 str_c
str_c(…, sep = “”, collapse = NULL)
- sep: 把多个字符串拼接为一个大的字符串，用于字符串的分割符；
- collapse: 把多个向量参数拼接为一个大的字符串，用于字符串的分割符。
str_c(c('a','a1'),c('b','b1'),sep='-')## [1] "a-b" "a1-b1"str_c(letters[1:5], " is for", "...") ## [1] "a is for..." "b is for..." "c is for..." "d is for..." "e is for..."str_c('a','b',sep='-')#sep可设置连接符## [1] "a-b"str_c('a','b',collapse = "-") # collapse参数，对多个字符串无效## [1] "ab"str_c(c('a','a1'),c('b','b1'),collapse='-') ## [1] "ab-a1b1"str_c(head(letters), collapse = "") #把多个向量参数拼接为一个大的字符串## [1] "abcdef"str_c(head(letters), collapse = ", ")## [1] "a, b, c, d, e, f"str_c(letters[-26], " comes before ", letters[-1])## [1] "a comes before b" "b comes before c" "c comes before d"
## [4] "d comes before e" "e comes before f" "f comes before g"
## [7] "g comes before h" "h comes before i" "i comes before j"
## [10] "j comes before k" "k comes before l" "l comes before m"
## [13] "m comes before n" "n comes before o" "o comes before p"
## [16] "p comes before q" "q comes before r" "r comes before s"
## [19] "s comes before t" "t comes before u" "u comes before v"
## [22] "v comes before w" "w comes before x" "x comes before y"
## [25] "y comes before z"str_c(letters)## [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q"
## [18] "r" "s" "t" "u" "v" "w" "x" "y" "z"str_c VS. paste
sep行为不一致，str_c无空格
str_c('a','b')## [1] "ab"paste('a','b')## [1] "a b"collapse行为一致
str_c(letters, collapse = "")## [1] "abcdefghijklmnopqrstuvwxyz"paste(letters, collapse = "")## [1] "abcdefghijklmnopqrstuvwxyz"对于空值处置不一致
str_c(c("a", NA, "b"), "-d")## [1] "a-d" NA "b-d"paste(c("a", NA, "b"), "-d")## [1] "a -d" "NA -d" "b -d"2.1.2 str_trim 去掉字符串空格和TAB
str_trim(string, side = c(“both”, “left”, “right”))
2.1.3 str_pad 补充字符串长度
str_pad(string, width, side = c(“left”, “right”, “both”), pad = " “)
- string: 字符串，字符串向量；
- width: 字符串填充后的长度；
- side: 填充方向，both两边都填充，left左边填充，right右边填充；
- pad: 用于填充的字符；
2.1.3 str_dup复制字符串
str_dup(string, times)
val <- c("abca4", 123, "cba2")
str_dup(val, 2)## [1] "abca4abca4" "123123" "cba2cba2"按位置复制
str_dup(val, 1:3)## [1] "abca4" "123123" "cba2cba2cba2"2.1.4 str_wrap 控制字符串输出格式
- string: 字符串，字符串向量。
- width: 设置一行所占的宽度。
- indent: 段落首行的缩进值
- exdent: 设置第二行后每行缩进
2.1.5 str_sub 截取字符串
str_sub(string, start = 1L, end = -1L)
- string: 字符串，字符串向量。
- start : 开始位置
- end : 结束位置
str_sub(string, start = 1L, end = -1L) 提取子字符串
str_sub(string, start = 1L, end = -1L) <- value 替换子字符串
txt <- "I am a little bird"
str_sub(txt, 1, 4) # 截取1-4的索引位置的字符串## [1] "I am"str_sub(txt, end=6) # 截取1-6的索引位置的字符串## [1] "I am a"str_sub(txt, 6) # 截取6到结束的索引位置的字符串## [1] "a little bird"str_sub(txt, c(1, 4), c(6, 8)) # 分2段截取字符串## [1] "I am a" "m a l"str_sub(txt, -3) # 通过负坐标截取字符串## [1] "ird"str_sub(txt, end = -3)## [1] "I am a little bi"x <- "AAABBBCCC" #对截取的字符串进行赋值。
str_sub(x, 1, 1) <- 1; x ## 在字符串的1的位置赋值为1## [1] "1AABBBCCC"str_sub(x, 2, -2) <- "2345"; x ## 在字符串从2到-2的位置赋值为2345## [1] "12345C"2.2 字符串计算函数
2.2.1 str_count, 字符串计数
str_count(string, pattern = “”)
- string: 字符串，字符串向量。
- pattern: 匹配的字符。
words <- c("These are some words.")
str_count(words)## [1] 21统计单词个数
str_count(words, boundary("word"))## [1] 4str_split(words, " ")[[1]]## [1] "These" "are" "some" "words."str_split(words, boundary("word"))[[1]]## [1] "These" "are" "some" "words"string<-c('ning xiao li','zhang san','zhao guo nan')
str_count(string,'i')## [1] 3 0 02.2.2 str_length，字符串长度
str_length(c("I", "am", "宁小丽", NA))## [1] 1 2 3 NA2.2.3 str_sort，字符串排序
- str_sort(x, decreasing = FALSE, na_last = TRUE, locale = “”, …)
- str_order(x, decreasing = FALSE, na_last = TRUE, locale = “”, …)
locale:按哪种语言习惯排序
str_order(c('wo','love','five','stars','red','flag'),locale = "en") ## [1] 3 6 2 5 4 1str_sort(c('wo','love','five','stars','red','flag'),locale = "en") # 按ASCII字母排序## [1] "five" "flag" "love" "red" "stars" "wo"str_sort(c('wo','love','five','stars','red','flag'),,decreasing=TRUE) # 倒序排序## [1] "wo" "stars" "red" "love" "flag" "five"str_sort(c('我','爱','五','星','红','旗'),locale = "zh") # 按拼音排序## [1] "爱" "红" "旗" "我" "五" "星"2.3 字符串匹配函数
2.3.1 str_split,字符串分割
- str_split(string, pattern, n = Inf)
- str_split_fixed(string, pattern, n)
参数列表：
- string: 字符串，字符串向量。
- pattern: 匹配的字符。
- n: 分割个数 #最后一组就不会被分割
val <- "abc,123,234,iuuu"
s1<-str_split(val, ",");s1## [[1]]
## [1] "abc" "123" "234" "iuuu"s2<-str_split(val, ",",2);s2## [[1]]
## [1] "abc" "123,234,iuuu"class(s1)## [1] "list"s3<-str_split_fixed(val, ",",2);s3## [,1] [,2]
## [1,] "abc" "123,234,iuuu"class(s3)## [1] "matrix"2.3.2 str_subset:返回的匹配字符串
str_subset(string, pattern)
string: 字符串，字符串向量。 pattern: 匹配的字符。
fruit <- c("apple", "banana", "pear", "pinapple")
str_subset(fruit, "a") ## 全文匹配## [1] "apple" "banana" "pear" "pinapple"str_subset(fruit, "ap") ##返回含字符'ap'的单词## [1] "apple" "pinapple"str_subset(fruit, "^a") ## 开头匹配## [1] "apple"str_subset(fruit, "a$") ## 结尾匹配## [1] "banana"str_subset(fruit, "b") ##返回含字符'b'的单词## [1] "banana"str_subset(fruit, "[aeiou]") ##返回含'aeiou'任一个字符的单词## [1] "apple" "banana" "pear" "pinapple"str_subset(c("a", NA, "b"), ".") #丢弃空值## [1] "a" "b"string <- 'My name is ABDATA, I’m 27.'
str_sub(string, -3,-2) <- 25; string## [1] "My name is ABDATA, I’m 25."str_subset()函数与word()函数的区别在于前者提取字符串的子串，后者提取的是单词,而且str_sub也可以其替换的作用。
2.3.3 word, 从文本中提取单词（适用于英语环境下的使用）
函数定义：word(string, start = 1L, end = start, sep = fixed(" “))
参数列表：
- string: 字符串，字符串向量。
- start: 开始位置。
- end: 结束位置。
- sep: 匹配字符。
2.3.4 str_detect匹配字符串的字符
函数定义：str_detect(string, pattern)
参数列表： - string: 字符串，字符串向量。 - pattern: 匹配字符。
val <- c("abca4", 123, "cba2")
str_detect(val, "a")## [1] TRUE FALSE TRUEstr_detect(val, "^a")## [1] TRUE FALSE FALSEstr_detect(val, "a$")## [1] FALSE FALSE FALSE2.3.5 str_match,从字符串中提取匹配组
函数定义：
- str_match(string, pattern)
- str_match_all(string, pattern)
参数列表：
- string: 字符串，字符串向量。
- pattern: 匹配字符。
val <- c("abc", 123, "cba") # 从字符串中提取匹配组
str_match(val, "a")## [,1]
## [1,] "a"
## [2,] NA
## [3,] "a"str_match(val, "[0-9]") # 匹配字符0-9，限1个，并返回对应的字符## [,1]
## [1,] NA
## [2,] "1"
## [3,] NAstr_match(val, "[0-9]*") # 匹配字符0-9，不限数量，并返回对应的字符## [,1]
## [1,] ""
## [2,] "123"
## [3,] ""str_match_all(val, "a") #从字符串中提取匹配组，以字符串matrix格式返回## [[1]]
## [,1]
## [1,] "a"
##
## [[2]]
## [,1]
##
## [[3]]
## [,1]
## [1,] "a"str_match_all(val, "[0-9]")## [[1]]
## [,1]
##
## [[2]]
## [,1]
## [1,] "1"
## [2,] "2"
## [3,] "3"
##
## [[3]]
## [,1]2.3.6 str_replace，字符串替换
函数定义：str_replace(string, pattern, replacement)
参数列表：
- string: 字符串，字符串向量。
- pattern: 匹配字符。
- replacement: 用于替换的字符。
val <- c("abc", 123, "cba")
str_replace(val, "[ab]", "-") #替换第一个匹配的字符# 把目标字符串第一个出现的a或b，替换为-## [1] "-bc" "123" "c-a"str_replace_all(val, "[ab]", "-") #替换所有匹配的字符 # 把目标字符串所有出现的a或b，替换为-## [1] "--c" "123" "c--"str_replace_all(val, "[a]", "\1\1") # 把目标字符串所有出现的a，替换为被转义的字符## [1] "\001\001bc" "123" "cb\001\001"2.3.7 str_replace_na把NA替换为NA字符串
str_replace_na(string, replacement = “NA”)
2.3.8 str_locate，找到的模式在字符串中的位置
val## [1] "abc" "123" "cba"str_locate(val, "a")## start end
## [1,] 1 1
## [2,] NA NA
## [3,] 3 3str_locate(val, c("a", 12, "b"))## start end
## [1,] 1 1
## [2,] 1 2
## [3,] 2 2str_locate_all(val, "a")## [[1]]
## start end
## [1,] 1 1
##
## [[2]]
## start end
##
## [[3]]
## start end
## [1,] 3 3str_locate_all(val, "[ab]")## [[1]]
## start end
## [1,] 1 1
## [2,] 2 2
##
## [[2]]
## start end
##
## [[3]]
## start end
## [1,] 2 2
## [2,] 3 32.3.9 str_extract从字符串中提取匹配模式
函数定义：
- str_extract(string, pattern)
- str_extract_all(string, pattern, simplify = FALSE)
参数列表：
- string: 字符串，字符串向量;
- pattern: 匹配字符;
- simplify: 返回值，TRUE返回matrix，FALSE返回字符串向量;
shopping_list <- c("apples 4x4", "bag of flour", "bag of sugar", "milk x2") str_extract(shopping_list, "\\d") # 提取数字 #提取匹配模式的第一个字符串## [1] "4" NA NA "2"str_extract(shopping_list, "[a-z]+") #提取字母## [1] "apples" "bag" "bag" "milk"str_extract_all(shopping_list, "[a-z]+") # 提取所有匹配模式的字母，结果返回一个列表## [[1]]
## [1] "apples" "x"
##
## [[2]]
## [1] "bag" "of" "flour"
##
## [[3]]
## [1] "bag" "of" "sugar"
##
## [[4]]
## [1] "milk" "x"str_extract_all(shopping_list, "\\d") # 提取所有匹配模式的数字## [[1]]
## [1] "4" "4"
##
## [[2]]
## character(0)
##
## [[3]]
## character(0)
##
## [[4]]
## [1] "2"str_extract_all(shopping_list, "\\b[a-z]+\\b", simplify = TRUE) ## [,1] [,2] [,3]
## [1,] "apples" "" ""
## [2,] "bag" "of" "flour"
## [3,] "bag" "of" "sugar"
## [4,] "milk" "" ""str_extract_all(shopping_list, "\\d", simplify = TRUE)## [,1] [,2]
## [1,] "4" "4"
## [2,] "" ""
## [3,] "" ""
## [4,] "2" ""str_extract(string, pattern) 提取匹配的第一个字符串
str_extract_all(string, pattern, simplify = FALSE) 提取匹配的所有字符串
功能与str_match(),str_match_all()函数类似
2.4 字符串变换函数
2.4.1 字符串编码转换
str_conv(string, encoding)
参数列表：
- string: 字符串，字符串向量。
- encoding: 编码名。
x <- charToRaw('你好');x## [1] c4 e3 ba c3str_conv(x, "GBK")## [1] "你好"str_conv(x, "GB2312")## [1] "你好"str_conv(x, "UTF-8")## Warning in stri_conv(string, encoding, "UTF-8"): input data \xffffffc4 in
## current source encoding could not be converted to Unicode## Warning in stri_conv(string, encoding, "UTF-8"): input data
## \xffffffe3\xffffffba in current source encoding could not be converted to
## Unicode## Warning in stri_conv(string, encoding, "UTF-8"): input data \xffffffc3 in
## current source encoding could not be converted to Unicode## [1] "<U+FFFD><U+FFFD><U+FFFD>"Unicode转UTF-8
x1 <- "\u5317\u4eac"
str_conv(x1, "UTF-8")## [1] "北京"2.4.2 str_to_upper,字符串大写转换
- str_to_upper(string, locale = “”)
- str_to_lower(string, locale = “”)
- str_to_title(string, locale = “”)
val <- "I am conan. Welcome to my blog! http://fens.me"
str_to_upper(val)## [1] "I AM CONAN. WELCOME TO MY BLOG! HTTP://FENS.ME"str_to_lower(val)## [1] "i am conan. welcome to my blog! http://fens.me"str_to_title(val)## [1] "I Am Conan. Welcome To My Blog! Http://Fens.me"3. 正则表达式
3.1 转义字符
- NUL字符（000）
- 制表符（009）
- 换行符（00A）
- 直制表符（00B）
- 换页符（00C）
- 回车符（00D）
- 十六进制拉丁字符
- 控制字符
3.2 字符类
- […] 方括号内任意字符
- [^...] 不在方括号内任意字符
- . 除换行符和其他unicode行终止符之外的任意字符
- 等价于[a-zA-Z0-9]
- 等价于[^a-zA-Z0-9]
- 任何unicode空白符
- 任何非unicode空白符
- 等价于[0-9]
- 等价于[^0-9]
- [] 退格
3.3 重复
- {n,m} 匹配前一项至少n次，不超过m次
- {n,} 匹配前一项至少n次
3.4 锚
- ^ 匹配字符串开头，多行匹配一行的开头
- $ 匹配字符串结尾，多行匹配一行的结尾
- 匹配一个单词的边界，位于
- 匹配非单词边界
- (?=p) 要求接下来的字符都与p匹配，但不能包括匹配p的那些字符
- (?!p) 要求接下来的字符不与p匹配
3.5 修饰符
- i，忽略大小写
- m，多行匹配模式
- g，全局匹配
3.6 选择、分组、引用
“|”与逻辑表达式中的或类似，前后两者任意一个匹配。
圆括号用来分组和引用 - {n} 匹配前一项n次 - ? 等价于{0,1} - + 等价于{1,} - * 等价于{0,}