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stringr

Jeason

2440字约8分钟

2019-08-18

字符串计算函数

str_length: 字符串长度 str_count: 字符串计数 str_order: 字符串排序

str_length,字符串长度

  • 函数定义：
str_length(string)
  • 参数列表：string: 字符串，字符串向量。
  • 使用示例：
> str_length(c("I", "am", NA))
[1]  1  2  2 NA

str_count, 字符串计数

  • 函数定义：
str_count(string, pattern = "")
  • 参数列表：string: 字符串，字符串向量。pattern: 匹配的字符。
  • 使用示例：

对字符串中匹配的字符计数

> str_count('aaa444sssddd', "a")
[1] 3

对字符串向量中匹配的字符计数

> fruit <- c("apple", "banana", "pear", "pineapple")
> str_count(fruit, "a")
[1] 1 3 1 1

对于一些特殊字符如："."，需要进行正则匹配

str_order, 字符串索引排序

  • 函数定义：
str_order(x, decreasing = FALSE, na_last = TRUE, locale = "en", numeric = FALSE, ...)  

str_sort(x, decreasing = FALSE, na_last = TRUE, locale = "en", numeric = FALSE, ...)
  • 参数列表：x: 字符串，字符串向量。decreasing: 排序方向。na_last:NA值的存放位置，一共3个值，TRUE放到最后，FALSE放到最前，NA过滤处理locale:按哪种语言习惯排序numeric: 是否只按照数字大小进行排序
  • 使用示例：
> str_sort(letters[1:5])
[1] "a" "b" "c" "d" "e"
> str_order(letters[1:5])
[1] 1 2 3 4 5

## 按照数字进行排序
> x <- c("100a10", "100a5", "2b", "2a")
> str_sort(x)
[1] "100a10" "100a5"  "2a"     "2b"  
> str_sort(x, numeric = TRUE)
[1] "2a"     "2b"     "100a5"  "100a10"

字符串拼接函数

str_c: 字符串拼接 str_trim: 去掉字符串的空格和TAB(\t) 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_c，字符串拼接

  • 函数定义：
str_c(..., sep = "", collapse = NULL)
  • 参数列表：…: 多参数的输入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
  • 使用示例：

把多个字符串拼接为一个大的字符串。

> str_c('a','b')
[1] "ab"
> str_c('a','b',sep='-')
[1] "a-b"
> str_c(c('a','a1'),c('b','b1'),sep='-')
[1] "a-b"   "a1-b1"

把多个向量参数拼接为一个大的字符串。

> str_c(head(letters), collapse = "")
[1] "abcdef"
# collapse参数，对多个字符串无效
> str_c('a','b',collapse = "-")   
[1] "ab"
> str_c(c('a','a1'),c('b','b1'),collapse='-')
[1] "ab-a1b1"

拼接有NA值的字符串向量时，NA还是NA

> str_c(c("a", NA, "b"), "-d")
[1] "a-d" NA    "b-d"
# Use str_replace_NA to display literal NAs:
> str_c(str_replace_na(c("a", NA, "b")), "-d")
[1] "a-d"  "NA-d" "b-d"

str_flatten: 字符串快速拼接函数

  • 函数定义：
str_flatten(string, collapse = "")
  • 参数列表：string: 字符串，字符串向量collapse: 拼接字符串之间插入的字符
  • 使用示例：
> str_flatten(letters)
[1] "abcdefghijklmnopqrstuvwxyz"
> str_flatten(letters, "-")
[1] "a-b-c-d-e-f-g-h-i-j-k-l-m-n-o-p-q-r-s-t-u-v-w-x-y-z"

str_trim:去掉字符串的空格和TAB(\t)

str_trim() 从字符串的开头和结尾删除空格; str_squish() 同时还可以删除字符串内部的空格

  • 函数定义：
str_trim(string, side = c("both", "left", "right"))
str_squish(string)
  • 参数列表：string: 字符串，字符串向量side: 过滤方式，both两边都过滤，left左边过滤，right右边过滤
  • 使用示例：
> str_trim("\n\nString with trailing and leading white space\n\n")
[1] "String with trailing, middle, and leading white space"
> str_squish("\n\nString with excess, trailing and leading white space\n\n")
[1] "String with trailing, middle, and leading white space"

str_pad:补充字符串的长度

  • 函数定义：
str_pad(string, width, side = c("left", "right", "both"), pad = " ")
  • 参数列表：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
  • 使用示例：
# 从左边补充空格，直到字符串长度为20
> str_pad("conan", 20, "left")
[1] "               conan"

# 从右边补充空格，直到字符串长度为20
> str_pad("conan", 20, "right")
[1] "conan               "

# 从左右两边各补充空格，直到字符串长度为20
> str_pad("conan", 20, "both")
[1] "       conan        "

# 从左右两边各补充x字符，直到字符串长度为20
> str_pad("conan", 20, "both",'x')
[1] "xxxxxxxconanxxxxxxxx"

str_dup: 复制字符串

  • 函数定义：
str_dup(string, times)
  • 参数列表：string: 字符串，字符串向量times: 复制数量
  • 使用示例：
> fruit <- c("apple", "pear", "banana")
> str_dup(fruit, 2)
[1] "appleapple"   "pearpear"     "bananabanana"

str_wrap，控制字符串输出格式

  • 函数定义：
str_wrap(string, width = 80, indent = 0, exdent = 0)
  • 参数列表： 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: 段落非首行的缩进值

str_sub,截取字符串

  • 函数定义：
str_sub(string, start = 1L, end = -1L)
str_sub(string, start = 1L, end = -1L, omit_na = FALSE) <- value
  • 参数列表：string: 字符串，字符串向量start : 开始位置end : 结束位置
  • 使用示例：
> hw <- "Hadley Wickham"
> str_sub(hw, 1, 6)
[1] "Hadley"
> str_sub(hw, end = 6)
[1] "Hadley"
> str_sub(hw, c(1, 8), c(6, 14))
[1] "Hadley"  "Wickham"

> str_sub(hw, -1)
[1] "m"
> str_sub(hw, -7)
[1] "Wickham"
> str_sub(hw, end = -7)
[1] "Hadley W"

字符串匹配函数

str_split: 字符串分割 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_replace: 字符串替换 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_extract: 从字符串中提取匹配字符

str_split,字符串分割

  • 函数定义：
str_split(string, pattern, n = Inf, simplify = FALSE)
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simplify: FALSE以list返回结果，TRUE以matrix返回结果
  • 使用示例：
> fruits <- c("apples and oranges and pears and bananas", "pineapples and mangos and guavas")
> str_split(fruits, " and ")
[[1]]
[1] "apples"  "oranges" "pears"   "bananas"

[[2]]
[1] "pineapples" "mangos"     "guavas"  

> str_split(fruits, " and ", simplify = TRUE)
     [,1]         [,2]      [,3]     [,4]   
[1,] "apples"     "oranges" "pears"  "bananas"
[2,] "pineapples" "mangos"  "guavas" "" 

> str_split(fruits, " and ", n = 3)
[[1]]
[1] "apples"            "oranges"           "pears and bananas"

[[2]]
[1] "pineapples" "mangos"     "guavas" 

> str_split_fixed(fruits, " and ", 3)
     [,1]         [,2]      [,3]             
[1,] "apples"     "oranges" "pears and bananas"
[2,] "pineapples" "mangos"  "guavas"         
> str_split_fixed(fruits, " and ", 4)
     [,1]         [,2]      [,3]     [,4]   
[1,] "apples"     "oranges" "pears"  "bananas"
[2,] "pineapples" "mangos"  "guavas" ""

str_subset:返回的匹配字符串

  • 函数定义：
str_subset(string, pattern, negate = FALSE)
str_which(string, pattern, negate = FALSE)
  • 参数列表:string: 字符串，字符串向量pattern: 匹配的字符negate: 如果为TRUE，返回未匹配的元素
  • 使用示例：
> fruit <- c("apple", "banana", "pear", "pinapple")
> str_subset(fruit, "a")
[1] "apple"    "banana"   "pear"     "pinapple"
> str_which(fruit, "a")
[1] 1 2 3 4
# 支持正则表达式
> str_subset(fruit, "^a")
[1] "apple"
> str_subset(fruit, "a$")
[1] "banana"

word, 从文本中提取单词

  • 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
  • 使用示例：
> sentences <- c("Jane saw a cat", "Jane sat down")
> word(sentences, 1)
[1] "Jane" "Jane"
> word(sentences, 2)
[1] "saw" "sat"
> word(sentences, -1)
[1] "cat"  "down"
> word(sentences, 2, -1)
[1] "saw a cat" "sat down" 
# 匹配以..分割开的word
> str <- 'abc.def..123.4568.999'
> word(str, 1, sep = fixed('..'))
[1] "abc.def"

str_detect，检查字符串是否出现

  • 函数定义：
str_detect(string, pattern, negate = FALSE)
  • 参数列表：string: 字符串，字符串向量pattern: 匹配字符negate: 如果为TRUE，返回未匹配的元素
  • 使用示例：
> fruit <- c("apple", "banana", "pear", "pinapple")
> str_detect(fruit, "a")
[1] TRUE TRUE TRUE TRUE
> str_detect(fruit, "^a")
[1]  TRUE FALSE FALSE FALSE
> str_detect(fruit, "^p", negate = TRUE)
[1]  TRUE  TRUE FALSE FALSE

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
  • 使用示例：
> val <- c("abc", 123, "cba")
> str_match(val, "a")
     [,1]
[1,] "a" 
[2,] NA  
[3,] "a" 
> str_match(val, "[0-9]")
     [,1]
[1,] NA  
[2,] "1" 
[3,] NA  
> str_match_all(val, "a")
[[1]]
     [,1]
[1,] "a" 

[[2]]
     [,1]

[[3]]
     [,1]
[1,] "a"

str_replace，字符串替换

  • 函数定义：
str_replace(string, pattern, replacement)
str_replace_all(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
  • 使用示例：
> fruits <- c("one apple", "two pears", "three bananas")
> str_replace(fruits, "[aeiou]", "-")
[1] "-ne apple"     "tw- pears"     "thr-e bananas"
> str_replace_all(fruits, "[aeiou]", "-")
[1] "-n- -ppl-"     "tw- p--rs"     "thr-- b-n-n-s"

str_replace_na把NA替换为NA字符串

  • 函数定义：
str_replace_na(string, replacement = "NA")
  • 参数列表：string: 字符串，字符串向量replacement : 用于替换的字符
  • 使用示例：
> str_replace_na(c(NA, "abc", "def"))
[1] "NA"  "abc" "def"

str_locate，找到的模式在字符串中的位置

  • 函数定义：
str_locate(string, pattern)
str_locate_all(string, pattern)
  • 参数列表：string: 字符串，字符串向量pattern: 匹配字符
  • 使用示例：
> fruit <- c("apple", "banana", "pear", "pineapple")
> str_locate(fruit, "a") # 在每个字符串中a的位置
     start end
[1,]     1   1
[2,]     2   2
[3,]     3   3
[4,]     5   5
> str_locate_all(fruit, "a") # 在每个字符串中所有a的位置
[[1]]
     start end
[1,]     1   1

[[2]]
     start end
[1,]     2   2
[2,]     4   4
[3,]     6   6

[[3]]
     start end
[1,]     3   3

[[4]]
     start end
[1,]     5   5

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
  • 使用示例：
> shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2")
> str_extract(shopping_list, "\\d")
[1] "4" NA  NA  "2"
> str_extract_all(shopping_list, "\\d")
[[1]]
[1] "4"

[[2]]
character(0)

[[3]]
character(0)

[[4]]
[1] "2"

> str_extract_all(shopping_list, "\\d", simplify = TRUE)
     [,1]
[1,] "4" 
[2,] ""  
[3,] ""  
[4,] "2"

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

str_conv:字符编码转换

  • 函数定义：
str_conv(string, encoding)
  • 参数列表：string: 字符串，字符串向量encoding: 编码名
  • 使用示例：
> x <- charToRaw('你好')
> x
[1] e4 bd a0 e5 a5 bd
> str_conv(x, "GBK")
[1] "你好"
> str_conv(x, "GB2312")
[1] "你好"

str_to_upper,字符串大写转换

  • 函数定义：
str_to_upper(string, locale = "en")
str_to_lower(string, locale = "en")
str_to_title(string, locale = "en")
str_to_sentence(string, locale = "en")
  • 参数列表：string: 字符串locale:按哪种语言习惯排序
  • 使用示例：
> dog <- "The quick brown dog"
> str_to_upper(dog)
[1] "THE QUICK BROWN DOG"
> str_to_lower(dog)
[1] "the quick brown dog"
> str_to_title(dog)
[1] "The Quick Brown Dog"
> str_to_sentence("the quick brown dog")
[1] "The quick brown dog"