regex - R 正则表达式 : how to remove "*" only in between a group of variables

Question

我有一组变量 var :

> var
[1] "a1" "a2" "a3" "a4"

这是我想要实现的目标:使用正则表达式并更改如下字符串:

 3*a1 + a1*a2 + 4*a3*a4 + a1*a3

到

 3a1 + a1*a2 + 4a3*a4 + a1*a3

基本上，我想修剪不在 var 中的任何值之间的“*” .先感谢您

Answer 1

可以做找(?<![\da-z])(\d+)\*替换 $1

 (?<! [\da-z] )
 ( \d+ )                       # (1)
 \*

或者， ((?:[^\da-z]|^)\d+)\*对于断言受损的引擎

 (                             # (1 start)
      (?: [^\da-z] | ^ )
      \d+ 
 )                             # (1 end)
 \*

无论如何，领先的断言都是不好的。

Benchmark

Regex1:   (?<![\da-z])(\d+)\*
Options:  < none >
Completed iterations:   100  /  100     ( x 1000 )
Matches found per iteration:   2
Elapsed Time:    1.09 s,   1087.84 ms,   1087844 µs


Regex2:   ((?:[^\da-z]|^)\d+)\*
Options:  < none >
Completed iterations:   100  /  100     ( x 1000 )
Matches found per iteration:   2
Elapsed Time:    0.77 s,   767.04 ms,   767042 µs