R語言中字符串的處理(3/3)-匹配查詢

本文轉(zhuǎn)自微信公眾號: 一遇之見 的 大作 R中字符串處理：函數(shù)實現(xiàn) 。原文太長，分三次學(xué)習(xí)、消化。

字符串匹配查詢

函數(shù)match、grep，grepl，str_detect，str_locate和str_locate_all，str_match和str_match_all均可實現(xiàn)字符串的匹配查詢，但有略有不同。函數(shù)match可實現(xiàn)多對多的完全匹配，但同一個值僅能返回到第一次匹配到的位置索引值；其它函數(shù)則可實現(xiàn)完全或者部分匹配。

字符串匹配查詢.png

match function

match("cd", c("ab", "cd", "ef", "mn"))   # 完全匹配
# [1] 2
match("cd", c("ab", "cdx", "ef", "mn"))  # 部分匹配不能實現(xiàn)
# [1] NA
match("cd", c("ab", "cd", "ef", "cd", "mn"))  # 僅返回第一次被匹配到的位置向量
# [1] 2
match(c("cd", "mn"), c("ab", "cd", "ef", "mn"))
# [1] 2 4
match(c("cd", "mn"), c("ab", "cd", "ef", "cd", "mn"))
# [1] 2 5

grep and grepl function

grep("cd", c("cxcx", "mn", "mn", "cd", "ef", "mn", "cxcx")) # 完全匹配
# [1] 4
grep("cd", c("cxcx", "mn", "mn", "cdxcdx", "ef", "mn", "cxcx")) # 部分匹配
# [1] 4
grep("cd", c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx")) # 一對多完全或部分匹配查詢，有幾個匹配幾個
# [1] 1 4 7
grep(c("cd", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx")) # 多對多完全或部分匹配查詢，其實只有第一個"cd"參與了匹配
# [1] 1 4 7     # Warning message:only the first element will be used

grepl("cd", c("cxcx", "mn", "mn", "cd", "ef", "mn", "cxcx")) # 完全匹配
# [1] FALSE FALSE FALSE  TRUE FALSE FALSE FALSE
grepl("cd", c("cxcx", "mn", "mn", "cdxcdx", "ef", "mn", "cxcx")) # 部分匹配
# [1] FALSE FALSE FALSE  TRUE FALSE FALSE FALSE
grepl("cd", c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx")) # 一對多完全或部分匹配，有幾個匹配幾個
# [1]  TRUE FALSE FALSE  TRUE FALSE FALSE  TRUE
grepl(c("cd", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx")) # 多對多完全或部分匹配查詢，其實只有第一個"cd"參與了匹配
# [1]  TRUE FALSE FALSE  TRUE FALSE FALSE  TRUE   # Warning message: only the first element will be used

str_detect function

str_detect(c("cd", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"))
# [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE
# Warning message:
# In stri_detect_regex(string, pattern, negate = negate, opts_regex = opts(pattern)) :
#  longer object length is not a multiple of shorter object length

str_detect(c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"), c("cd", "mn"))
# [1]  TRUE  TRUE FALSE FALSE FALSE  TRUE  TRUE  TRUE  TRUE
# Warning message:
# In stri_detect_regex(string, pattern, negate = negate, opts_regex = opts(pattern)) :
#  longer object length is not a multiple of shorter object length

str_locate and str_locate_all function

str_locate(c("cd", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"))
#       start end
# [1,]    NA  NA
# [2,]    NA  NA
# [3,]    NA  NA
# [4,]    NA  NA
# [5,]    NA  NA
# [6,]    NA  NA
# [7,]    NA  NA
# [8,]     1   2
# [9,]     1   2
# Warning message:
# In stri_locate_first_regex(string, pattern, opts_regex = opts(pattern)) :
#   longer object length is not a multiple of shorter object length

str_locate(c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"), c("cd", "mn"))
#       start end
# [1,]     1   2
# [2,]     1   2
# [3,]    NA  NA
# [4,]    NA  NA
# [5,]    NA  NA
# [6,]     1   2
# [7,]     1   2
# [8,]     1   2
# [9,]     1   2
# Warning message:
# In stri_locate_first_regex(string, pattern, opts_regex = opts(pattern)) :
#  longer object length is not a multiple of shorter object length

str_locate_all(c("cd", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"))
# [[1]]
# start end
# 
# [[2]]
# start end
# 
# [[3]]
# start end
# 
# [[4]]
# start end
# 
# [[5]]
# start end
# 
# [[6]]
# start end
# 
# [[7]]
# start end
# 
# [[8]]
# start end
# [1,]     1   2
# 
# [[9]]
# start end
# [1,]     1   2
# 
# Warning message:
#   In stri_locate_all_regex(string, pattern, omit_no_match = TRUE,  :
#                              longer object length is not a multiple of shorter object length

str_locate_all(c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"), c("cd", "mn"))
# [[1]]
# start end
# [1,]     1   2
# [2,]     4   5
# 
# [[2]]
# start end
# [1,]     1   2
# 
# [[3]]
# start end
# 
# [[4]]
# start end
# 
# [[5]]
# start end
# 
# [[6]]
# start end
# [1,]     1   2
# 
# [[7]]
# start end
# [1,]     1   2
# [2,]     4   5
# 
# [[8]]
# start end
# [1,]     1   2
# 
# [[9]]
# start end
# [1,]     1   2
# 
# Warning message:
#   In stri_locate_all_regex(string, pattern, omit_no_match = TRUE,  :
#                              longer object length is not a multiple of shorter object length

str_match and str_match_all function (in stringr package)

str_match(c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"), c("cdx", "mn"))
# [,1] 
# [1,] "cdx"
# [2,] "mn" 
# [3,] NA   
# [4,] NA   
# [5,] NA   
# [6,] "mn" 
# [7,] "cdx"
# [8,] "mn" 
# [9,] NA   
# Warning message:
#   In stri_match_first_regex(string, pattern, opts_regex = opts(pattern)) :
#   longer object length is not a multiple of shorter object length

str_match(c("cdx", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"))
# [,1]
# [1,] NA  
# [2,] NA  
# [3,] NA  
# [4,] NA  
# [5,] NA  
# [6,] NA  
# [7,] NA  
# [8,] "mn"
# [9,] "cd"
# Warning message:
#   In stri_match_first_regex(string, pattern, opts_regex = opts(pattern)) :
#   longer object length is not a multiple of shorter object length

str_match_all(c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"), c("cdx", "mn"))
# [[1]]
# [,1] 
# [1,] "cdx"
# [2,] "cdx"
# 
# [[2]]
# [,1]
# [1,] "mn"
# 
# [[3]]
# [,1]
# 
# [[4]]
# [,1]
# 
# [[5]]
# [,1]
# 
# [[6]]
# [,1]
# [1,] "mn"
# 
# [[7]]
# [,1] 
# [1,] "cdx"
# [2,] "cdx"
# 
# [[8]]
# [,1]
# [1,] "mn"
# 
# [[9]]
# [,1]
# 
# Warning message:
#   In stri_match_all_regex(string, pattern, omit_no_match = TRUE, opts_regex = opts(pattern)) :
#   longer object length is not a multiple of shorter object length

str_match_all(c("cdx", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"))
# [[1]]
# [,1]
# 
# [[2]]
# [,1]
# 
# [[3]]
# [,1]
# 
# [[4]]
# [,1]
# 
# [[5]]
# [,1]
# 
# [[6]]
# [,1]
# 
# [[7]]
# [,1]
# 
# [[8]]
# [,1]
# [1,] "mn"
# 
# [[9]]
# [,1]
# [1,] "cd"
# 
# Warning message:
#   In stri_match_all_regex(string, pattern, omit_no_match = TRUE, opts_regex = opts(pattern)) :
#   longer object length is not a multiple of shorter object length

str_extract and str_extract_all function

str_extract(c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"), c("cdx", "mn"))
# [1] "cdx" "mn"  NA    NA    NA    "mn"  "cdx" "mn"  NA   
# Warning message:
#   In stri_extract_first_regex(string, pattern, opts_regex = opts(pattern)) :
#   longer object length is not a multiple of shorter object length

str_extract(c("cdx", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"))
# [1] NA   NA   NA   NA   NA   NA   NA   "mn" "cd"
# Warning message:
#   In stri_extract_first_regex(string, pattern, opts_regex = opts(pattern)) :
#   longer object length is not a multiple of shorter object length

str_extract_all(c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"), c("cdx", "mn"))
# [[1]]
# [1] "cdx" "cdx"
# 
# [[2]]
# [1] "mn"
# 
# [[3]]
# character(0)
# 
# [[4]]
# character(0)
# 
# [[5]]
# character(0)
# 
# [[6]]
# [1] "mn"
# 
# [[7]]
# [1] "cdx" "cdx"
# 
# [[8]]
# [1] "mn"
# 
# [[9]]
# character(0)
# 
# Warning message:
#   In stri_extract_all_regex(string, pattern, simplify = simplify,  :
#                               longer object length is not a multiple of shorter object length

str_extract_all(c("cdx", "mn"), c("cdxcdx", "mny", "mn", "cd", "ef", "mnz", "cdxcdx", "mn", "cd"))
# [[1]]
# character(0)
# 
# [[2]]
# character(0)
# 
# [[3]]
# character(0)
# 
# [[4]]
# character(0)
# 
# [[5]]
# character(0)
# 
# [[6]]
# character(0)
# 
# [[7]]
# character(0)
# 
# [[8]]
# [1] "mn"
# 
# [[9]]
# [1] "cd"
# 
# Warning message:
#   In stri_extract_all_regex(string, pattern, simplify = simplify,  :
#                               longer object length is not a multiple of shorter object length

原文參考文章：
1.字符串處理
2.R語言字符串處理包stringr

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