删除最后一个字符，除非前面有特定字符

Been using R for a while but my regex skills are novice grade. I'm attempting to remove the "s" if its the final character in a word EXCEPT if its preceded by an "i" or an "s" for example. Sample...

一直使用R,但我的正则表达技能是新手等级。我试图删除“s”,如果它是单词中的最后一个字符,除非前面有“i”或“s”。样品...

dfx <- c("class","guests","trips","sassy","basis","fruits")
dfx <- sub("s$","",dfx)
View(dfx)

Any examples or guidance would be appreciated.

任何例子或指导将不胜感激。

2 个解决方案

#1

You can use lookarounds for this. I'm not the best at them, but check out this tutorial to learn more. For example (?<!s)s will match an "s" that is not preceded by an "s". Note you have to set perl=T for these to work in R.

你可以使用lookarounds。我不是最好的,但请查看本教程以了解更多信息。例如(?

sub("(?<!s|i)s$","",dfx,perl = T)
# [1] "class" "guest" "trip"  "sassy" "basis" "fruit"

#2

s(?<![is]s)\b is what's needed.

s(?

https://regex101.com/r/ANyYB0/1

Benchmark showing the right way and the wrong way

基准显示正确的方式和错误的方式

Regex1:   s(?<![is]s)\b
Completed iterations:   50  /  50     ( x 1000 )
Matches found per iteration:   3
Elapsed Time:    0.30 s,   295.43 ms,   295426 µs
Matches per sec:   507,741


Regex2:   (?<![is])s\b
Completed iterations:   50  /  50     ( x 1000 )
Matches found per iteration:   3
Elapsed Time:    0.72 s,   718.22 ms,   718215 µs
Matches per sec:   208,851

#1