R语言中字符串的处理(2/3) |
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本文转自微信公众号: 一遇之见 的 大作 R中字符串处理：函数实现 。原文太长，分三次学习、消化。 字符串分割函数：strsplit，str_split和str_split_fixed函数strsplit,str_split和str_split_fixed均可实现字符串的分割，但strsplit和str_split返回结果为列表，而str_split_fixed返回结果为矩阵。 fruits = c("Small Yellow Banana", " Red Apple", "Big Sweet Pear ", "Sour PineApple") strsplit(fruits, " ") # [[1]] # [1] "Small" "Yellow" "Banana" # [[2]] # [1] "" "Red" "Apple" # [[3]] # [1] "Big" "Sweet" "Pear" "" #其实这里是两个空格 # [[4]] # [1] "Sour" "PineApple" library(stringr) str_split(fruits, " ") # [[1]] # [1] "Small" "Yellow" "Banana" # [[2]] # [1] "" "Red" "Apple" # [[3]] # [1] "Big" "Sweet" "Pear" "" "" #这个函数识别出了两个空格 # [[4]] # [1] "Sour" "PineApple" str_split_fixed(fruits, " ", n = 3) # [,1] [,2] [,3] # [1,] "Small" "Yellow" "Banana" # [2,] "" "Red" "Apple" # [3,] "Big" "Sweet" "Pear " # [4,] "Sour" "PineApple" ""函数unlist可将函数strsplit和str_split返回结果列表转化为向量。 unlist(strsplit(fruits, " ")) # [1] "Small" "Yellow" "Banana" "" "Red" "Apple" # [7] "Big" "Sweet" "Pear" "" "Sour" "PineApple" unlist(str_split(author, " ")) unlist(str_split(fruits, " ")) # [1] "Small" "Yellow" "Banana" "" "Red" "Apple" # [7] "Big" "Sweet" "Pear" "" "" "Sour" # [13] "PineApple"三个字符串分割函数中，str_split_fixed的返回结果为数据框，方便对后期结果的引用。此外，函数str_split和str_split_fixed中都有参数n，但str_split中的参数可设置也可不设置，函数返回结果依旧是列表；str_split_fixed中参数n必须设置。其中参数n小于最大分割个数时，后面的不再分隔；参数n超过最大分割数时，后面内容为空。 str_split(fruits, " ", n = 2) # [[1]] # [1] "Small" "Yellow Banana" # [[2]] # [1] "" "Red Apple" # [[3]] # [1] "Big" "Sweet Pear " # [[4]] # [1] "Sour" "PineApple" str_split(fruits, " ", n = 5) # [[1]] # [1] "Small" "Yellow" "Banana" # [[2]] # [1] "" "Red" "Apple" # [[3]] # [1] "Big" "Sweet" "Pear" "" "" # [[4]] # [1] "Sour" "PineApple" str_split_fixed(fruits, " ", n = 3) # [,1] [,2] [,3] # [1,] "Small" "Yellow" "Banana" # [2,] "" "Red" "Apple" # [3,] "Big" "Sweet" "Pear " # [4,] "Sour" "PineApple" "" str_split_fixed(fruits, " ", n = 2) # [,1] [,2] # [1,] "Small" "Yellow Banana" # [2,] "" "Red Apple" # [3,] "Big" "Sweet Pear " # [4,] "Sour" "PineApple" str_split_fixed(fruits, " ", n = 5) # [,1] [,2] [,3] [,4] [,5] # [1,] "Small" "Yellow" "Banana" "" "" # [2,] "" "Red" "Apple" "" "" # [3,] "Big" "Sweet" "Pear" "" "" # [4,] "Sour" "PineApple" "" "" "" 字符串提取函数substr(x, start,stop)：对字符串x截取从start到stop的子字符串。 函数substring(text,first, last = 1000000L)：对字符串text截取从first到last的子字符串，last默认值为1000000，可以不传参。 str_sub(x, start = 1L, end = -1L)：对字符串x截取从start到end的子字符串，start和end有默认值，可以不传参。 txt 1 and only the first element will be used str_replace(c("HacHgd", "aeHfgH", "defg"), c("H","a"), c("I", "b")) ## [1] "IacHgd" "beHfgH" "defg" ## Warning in stri_replace_first_regex(string, pattern, ## fix_replacement(replacement), : longer object length is not a multiple of ## shorter object length gsub(c("H","a"), c("I", "b"),c("HacHgd", "aeHfgH", "defg")) ## [1] "IacIgd" "aeIfgI" "defg" ## Warning in gsub(c("H", "a"), c("I", "b"), c("HacHgd", "aeHfgH", "defg")): ## argument 'pattern' has length > 1 and only the first element will be used ## Warning in gsub(c("H", "a"), c("I", "b"), c("HacHgd", "aeHfgH", "defg")): ## argument 'replacement' has length > 1 and only the first element will be used str_replace_all(c("HacHgd", "aeHfgH", "defg"), c("H","a"), c("I", "b")) ## [1] "IacIgd" "beHfgH" "defg" ## Warning in stri_replace_all_regex(string, pattern, ## fix_replacement(replacement), : longer object length is not a multiple of ## shorter object length str_replace(c("HacHgd", "aeHfgH", "defg"), c("H","a","g", "d"), c("I", "b","H","e")) #此时返回结果长度为4 ## [1] "IacHgd" "beHfgH" "defH" "HacHge" ## Warning in stri_replace_first_regex(string, pattern, ## fix_replacement(replacement), : longer object length is not a multiple of ## shorter object length str_replace_all(c("HacHgd", "aeHfgH", "defg"), c("H","a","g", "d"), c("I", "b","H","e"))#此时返回结果长度为4 ## [1] "IacIgd" "beHfgH" "defH" "HacHge" ## Warning in stri_replace_all_regex(string, pattern, ## fix_replacement(replacement), : longer object length is not a multiple of ## shorter object length此外，函数str_repalce_all还可以实现多个字符串的同时替换(str_replac没有此功能)。 y = c(c("I", "b")) names(y) = c("H","a") str_replace_all(c("HacHgd", "aeHfgH", "defg"),y) ## [1] "IbcIgd" "beIfgI" "defg"针对函数str_repalce_all的多个字符串的同时替换功能，有时会出现意想不到的结果，而mgsub::mgsub可以产生另外一种结果。 y = c(c("a", "H")) names(y) = c("H","a") str_replace_all(c("HacHgd", "aeHfgH", "defg"),y) ## [1] "HHcHgd" "HeHfgH" "defg" mgsub::mgsub(c("HacHgd", "aeHfgH", "defg"), c("H","a"),c(c("a", "H"))) ## [1] "aHcagd" "Heafga" "defg" |
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