英文:
r - replace part of string after its matched
问题
我想替换一个字符串的一部分，该部分如以下示例所示：
str1 <- "abc sdak+ 123+"
我想替换所有在3个数字之后出现的+，但不替换在字符后出现的+。我尝试过这样，但这替换了整个匹配的字符串，而我只想将+替换为-：
gsub("[0-9]{3}\\+", "-", str1)
期望的结果应该是：
"abc sdak+ 123-"
英文:
i'm trying to replace a part of a string which is matched like in the following example:
str1 <- "abc sdak+ 123+"
I would like to replace all + that come after 3 numbers, but not in the case when a + is coming after characters. I tried like this, but this replaces the whole matched string, when I only want to replace the + with a -
gsub("[0-9]{3}\\+", "-", str1)
The desired outcome should be:
"abc sdak+ 123-"
答案1
得分: 2
可以捕获这3个数字作为一个组((...))以及+，然后用捕获组的反向引用(\\1)和-来替换它。只需确保在这3个数字之前没有其他数字，可以使用单词边界(\\b)或空格(\\s)。
gsub("\\b(\\d{3})\\+", "\-", str1)
输出
[1] "abc sdak+ 123-"
英文:
We could capture the 3 digits as a group ((...)) and the +, replace with the backreference (\\1) of the captured group and the -. Just to make sure that there is no digits before the 3 digits, use either word boundary (\\b) or a space (\\s)
gsub("\\b(\\d{3})\\+", "\-", str1)
-output
[1] "abc sdak+ 123-"
答案2
得分: 2
你也可以使用look-behind，即是否在3个数字之前有+符号？如果是的话，替换它。
str1 <- "abc sdak+ 123+"
gsub("(?<= [0-9]{3})\\+", "-", str1, perl = TRUE)
[1] "abc sdak+ 123-"
英文:
You can also use look-behind ie is the + symbol preceded by 3 numbers? if so, replace it.
str1 <- "abc sdak+ 123+"
gsub("(?<= [0-9]{3})\\+", "-", str1, perl = TRUE)
[1] "abc sdak+ 123-"
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