盘点R语言处理文本包stringr的特异功能
薛英杰 / 2022-04-26
使用R处理文本数据离不开正则表达式和得心应手的函数，stringr包配合正则表达式可以解决几乎所有文本分析中遇到的问题。今天我们就来盘点一下这个包中各个函数的特异功能。
1.查找文本中是否有要匹配字段
- str_detect(string,pattern): 探测文本中是否出现了某个字符
示例：
library(stringr)
fruit<-c("apple","pear","banana","orange")
str_detect(fruit,"a")
## [1] TRUE TRUE TRUE TRUE
str_detect(fruit,"ap")
## [1] TRUE FALSE FALSE FALSE
- str_which(string,pattern): 返回索要查找字符的索引
示例：
library(stringr)
fruit<-c("apple","pear","banana","orange")
str_which(fruit,"a")
## [1] 1 2 3 4
str_which(fruit,"ap")
## [1] 1
- str_count(string,pattern): 返回索要匹配字符在文本中出现的次数
示例：
library(stringr)
fruit<-c("apple","pear","banana","orange")
str_count(fruit,"a")
## [1] 1 1 3 1
str_count(fruit,"an")
## [1] 0 0 2 1
- str_locate(string,pattern): 返回索要查找的字符在文本中开始和终止的位置
示例：
library(stringr)
fruit<-c("apple","pear","banana","orange")
str_locate(fruit,"a")
## start end
## [1,] 1 1
## [2,] 3 3
## [3,] 2 2
## [4,] 3 3
str_locate(fruit,"an")
## start end
## [1,] NA NA
## [2,] NA NA
## [3,] 2 3
## [4,] 3 4
str_locate_all(fruit,"an")
## [[1]]
## start end
##
## [[2]]
## start end
##
## [[3]]
## start end
## [1,] 2 3
## [2,] 4 5
##
## [[4]]
## start end
## [1,] 3 4
Warning:注意str_locate和str_locate_all的区别，如果一个文本中有多个匹配目标文本，str_locate_all是返回所有目标文本的精确位置，而str_locate只返回第一个。
2.提取文本子集
- str_sub(string,start,end): 设定开始和结束长度来提前文本子集
示例：
library(stringr)
fruit<-c("apple","pear","banana","orange")
str_sub(fruit,1,3)
## [1] "app" "pea" "ban" "ora"
str_sub(fruit,-3,-1)
## [1] "ple" "ear" "ana" "nge"
- str_subset(string,pattern): 返回包含特定模式的字符集
示例：
library(stringr)
fruit<-c("apple","pear3","banana6","orange9")
str_subset(fruit,"an")
## [1] "banana6" "orange9"
str_subset(fruit,"\\d")
## [1] "pear3" "banana6" "orange9"
- str_extract(string,pattern): 返回匹配到特定模式的字符集
示例：
library(stringr)
fruit<-c("apple6","pear3","banana6","orange9")
str_extract(fruit,"an")
## [1] NA NA "an" "an"
str_extract(fruit,"\\d")
## [1] "6" "3" "6" "9"
- str_match(string,pattern): 返回匹配到特定模式的字符集
示例：
library(stringr)
fruit<-c("apple6","pear3","banana6","orange9")
str_match(fruit,"an")
## [,1]
## [1,] NA
## [2,] NA
## [3,] "an"
## [4,] "an"
str_match(fruit,"\\d")
## [,1]
## [1,] "6"
## [2,] "3"
## [3,] "6"
## [4,] "9"
Warning:注意str_match和str_extract的区别在于返回的数据类型不同，前者返回矩阵，后者返回向量。
3.字符长度处理
- str_pad(string,width,side,ellipsis): 用字符填充文本到固定长度
示例：
library(stringr)
fruit<-c("1","2","3","4")
str_pad(fruit,6,"left","0")
## [1] "000001" "000002" "000003" "000004"
- str_trunc(string,width,side,ellipsis): 截取固定width长度的 字符，截取部分用ellipsis替代
示例：
library(stringr)
fruit<-c("apple6","pear3","banana6","orange9")
str_trunc(fruit,2,"left","4")
## [1] "46" "43" "46" "49"
str_trunc(fruit,2,"center","4")
## [1] "a4apple6" "p4pear3" "b4banana6" "o4orange9"
str_trunc(fruit,2,"right","4")
## [1] "a4" "p4" "b4" "o4"
- str_trim(string,side): 删除字符左右两边的空白
示例：
library(stringr)
fruit<-c(" apple6"," pear3","banana6 ","orange9 ")
fruit
## [1] " apple6" " pear3" "banana6 " "orange9 "
str_trim(fruit,"left")
## [1] "apple6" "pear3" "banana6 " "orange9 "
str_trim(fruit,"both")
## [1] "apple6" "pear3" "banana6" "orange9"
str_trim(fruit,"right")
## [1] " apple6" " pear3" "banana6" "orange9"
4. 字符操作
- str_replace(string,pattern,replacement): 替代每个文本中第一次被匹配的字符
示例：
library(stringr)
fruit<-c(" apple6"," pear3","banana6 ","orange9 ")
fruit
## [1] " apple6" " pear3" "banana6 " "orange9 "
str_replace(fruit,"\\d","数字")
## [1] " apple数字" " pear数字" "banana数字 " "orange数字 "
- str_to_lower(string,pattern,replacement): 大写字母转换成小写
示例：
library(stringr)
fruit<-c("Apple6"," Pear3","Banana6 ",")range9 ")
fruit
## [1] "Apple6" " Pear3" "Banana6 " ")range9 "
str_to_lower(fruit)
## [1] "apple6" " pear3" "banana6 " ")range9 "
- str_to_upper(string,pattern,replacement): 小写字母转换成大写
示例：
library(stringr)
fruit<-c("Apple6"," Pear3","Banana6 ",")range9 ")
fruit
## [1] "Apple6" " Pear3" "Banana6 " ")range9 "
str_to_upper(fruit)
## [1] "APPLE6" " PEAR3" "BANANA6 " ")RANGE9 "
文本合并与拆分
- str_c(…,sep=“”,collapse=NULL): 文本合并
示例：
library(stringr)
fruit<-data.frame(ates=c("Apple6"," Pear3","Banana6 ","range9 "),
btas=c("Apple6"," Pear3","Banana6 ","range9 "))
str_c(fruit$ates,fruit$btas,collapse=NULL)
## [1] "Apple6Apple6" " Pear3 Pear3" "Banana6 Banana6 " "range9 range9 "
str_c(fruit$ates,fruit$btas,collapse="")
## [1] "Apple6Apple6 Pear3 Pear3Banana6 Banana6 range9 range9 "
Warning:注意参数collapse=““和collapse=NULL的区别。
- str_dup(string,time): 构造重复性文本
示例：
library(stringr)
fruit<-c("Apple6"," Pear3","Banana6 ","range9 ")
str_dup(fruit,3)
## [1] "Apple6Apple6Apple6" " Pear3 Pear3 Pear3"
## [3] "Banana6 Banana6 Banana6 " "range9 range9 range9 "
- str_split_fixed(string,pattern,n): 拆分一个文本向量成矩阵子文本
示例：
library(stringr)
fruit<-c("Apple6"," Pear3","Banana6 ","range9 ")
str_split_fixed(fruit,"e",2)
## [,1] [,2]
## [1,] "Appl" "6"
## [2,] " P" "ar3"
## [3,] "Banana6 " ""
## [4,] "rang" "9 "
str_split_fixed(fruit,"\\d",2)
## [,1] [,2]
## [1,] "Apple" ""
## [2,] " Pear" ""
## [3,] "Banana" " "
## [4,] "range" " "
str_split(fruit,"\\d")
## [[1]]
## [1] "Apple" ""
##
## [[2]]
## [1] " Pear" ""
##
## [[3]]
## [1] "Banana" " "
##
## [[4]]
## [1] "range" " "
- str_glue(string,pattern,n): 文本中嵌入数字并并计算
示例：
library(stringr)
bta<-1:4
fruit<-c("Apple6"," Pear3","Banana6 ","range9 ")
str_glue("{fruit} is {bta}")
## Apple6 is 1
## Pear3 is 2
## Banana6 is 3
## range9 is 4
文本排序
- str_order(string): 返回文本向量排序索引
示例：
library(stringr)
fruit<-c("Apple6"," Pear3","Banana6 ","range9 ")
str_order(fruit)
## [1] 2 1 3 4
- str_order(string): 返回文本向量排序后结果
示例：
library(stringr)
fruit<-c("Apple6"," Pear3","Banana6 ","range9 ")
str_sort(fruit)
## [1] " Pear3" "Apple6" "Banana6 " "range9 "