Question

我正在尝试替换字符串中的某个字符但是由于这种模式是重复发生的，我曾想过如果它甚至可能使用RegExes迭代替换它。例如，考虑一个链接http://www.bbc.co.uk/food/ingredients/by/letter/a

我想用'b'替换最后的'a'，然后用'c'，'d'替换，直到'z'迭代。使用RegEx可以很简单：

http:\/\/www\.bbc\.co\.uk\/food\/ingredients\/by\/letter\/[a-z]

这将验证字符串，但我想自动化链接生成过程。我对'R'很新，我想知道这样的事情是否可行。

Answer 1

您可以使用paste0创建如下链接列表：

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

导致以下列表：

> 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

提取目录名称（即/ a之前的所有内容），然后使用内置变量letters附加每个字母：

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

给出了这个字符向量：

 [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

另一种选择：

####

如何使用R

3 个答案: