如何使用R中的RegEx替換字符串中的字符

Question

我正在嘗試替換字符串中的某個字符但是由於這種模式反復發生，我曾想過如果可能的話，使用RegExes迭代替換它。 例如，請考慮鏈接http://www.bbc.co.uk/food/ingredients/by/letter/a

我想用'b'替換最后的'a'，然后用'c'，'d'替換，直到'z'迭代。 使用RegEx可以很簡單：

http:\\/\\/www\\.bbc\\.co\\.uk\\/food\\/ingredients\\/by\\/letter\\/[az]

這將驗證字符串，但我想自動化鏈接生成過程。 我對'R'很新，我想知道這樣的事情是否可行。

Answer 1

您可以使用paste0創建如下鏈接列表：

l <- paste0("http://www.bbc.co.uk/food/ingredients/by/letter/", letters)

這導致以下列表：

> l
 [1] "http://www.bbc.co.uk/food/ingredients/by/letter/a"
 [2] "http://www.bbc.co.uk/food/ingredients/by/letter/b"
 [3] "http://www.bbc.co.uk/food/ingredients/by/letter/c"
 [4] "http://www.bbc.co.uk/food/ingredients/by/letter/d"
 [5] "http://www.bbc.co.uk/food/ingredients/by/letter/e"
 [6] "http://www.bbc.co.uk/food/ingredients/by/letter/f"
 [7] "http://www.bbc.co.uk/food/ingredients/by/letter/g"
 [8] "http://www.bbc.co.uk/food/ingredients/by/letter/h"
 [9] "http://www.bbc.co.uk/food/ingredients/by/letter/i"
[10] "http://www.bbc.co.uk/food/ingredients/by/letter/j"
[11] "http://www.bbc.co.uk/food/ingredients/by/letter/k"
[12] "http://www.bbc.co.uk/food/ingredients/by/letter/l"
[13] "http://www.bbc.co.uk/food/ingredients/by/letter/m"
[14] "http://www.bbc.co.uk/food/ingredients/by/letter/n"
[15] "http://www.bbc.co.uk/food/ingredients/by/letter/o"
[16] "http://www.bbc.co.uk/food/ingredients/by/letter/p"
[17] "http://www.bbc.co.uk/food/ingredients/by/letter/q"
[18] "http://www.bbc.co.uk/food/ingredients/by/letter/r"
[19] "http://www.bbc.co.uk/food/ingredients/by/letter/s"
[20] "http://www.bbc.co.uk/food/ingredients/by/letter/t"
[21] "http://www.bbc.co.uk/food/ingredients/by/letter/u"
[22] "http://www.bbc.co.uk/food/ingredients/by/letter/v"
[23] "http://www.bbc.co.uk/food/ingredients/by/letter/w"
[24] "http://www.bbc.co.uk/food/ingredients/by/letter/x"
[25] "http://www.bbc.co.uk/food/ingredients/by/letter/y"
[26] "http://www.bbc.co.uk/food/ingredients/by/letter/z"

Answer 2

提取目錄名稱（即/ a之前的所有內容），然后使用內置變量letters附加每個letters ：

u <- "http://www.bbc.co.uk/food/ingredients/by/letter/a" # input string
file.path(dirname(u), letters)

它給出了這個字符向量：

 [1] "http://www.bbc.co.uk/food/ingredients/by/letter/a"
 [2] "http://www.bbc.co.uk/food/ingredients/by/letter/b"
 [3] "http://www.bbc.co.uk/food/ingredients/by/letter/c"
 [4] "http://www.bbc.co.uk/food/ingredients/by/letter/d"
 [5] "http://www.bbc.co.uk/food/ingredients/by/letter/e"
 [6] "http://www.bbc.co.uk/food/ingredients/by/letter/f"
 [7] "http://www.bbc.co.uk/food/ingredients/by/letter/g"
 [8] "http://www.bbc.co.uk/food/ingredients/by/letter/h"
 [9] "http://www.bbc.co.uk/food/ingredients/by/letter/i"
[10] "http://www.bbc.co.uk/food/ingredients/by/letter/j"
[11] "http://www.bbc.co.uk/food/ingredients/by/letter/k"
[12] "http://www.bbc.co.uk/food/ingredients/by/letter/l"
[13] "http://www.bbc.co.uk/food/ingredients/by/letter/m"
[14] "http://www.bbc.co.uk/food/ingredients/by/letter/n"
[15] "http://www.bbc.co.uk/food/ingredients/by/letter/o"
[16] "http://www.bbc.co.uk/food/ingredients/by/letter/p"
[17] "http://www.bbc.co.uk/food/ingredients/by/letter/q"
[18] "http://www.bbc.co.uk/food/ingredients/by/letter/r"
[19] "http://www.bbc.co.uk/food/ingredients/by/letter/s"
[20] "http://www.bbc.co.uk/food/ingredients/by/letter/t"
[21] "http://www.bbc.co.uk/food/ingredients/by/letter/u"
[22] "http://www.bbc.co.uk/food/ingredients/by/letter/v"
[23] "http://www.bbc.co.uk/food/ingredients/by/letter/w"
[24] "http://www.bbc.co.uk/food/ingredients/by/letter/x"
[25] "http://www.bbc.co.uk/food/ingredients/by/letter/y"
[26] "http://www.bbc.co.uk/food/ingredients/by/letter/z"

Answer 3

另外一個選項：

library(stringi)
v <- "http://www.bbc.co.uk/food/ingredients/by/letter/a"
stri_replace_last(v, letters, regex = "[a-z]")