Extract position of "+" and "*" symbol in string using R

Question

I am looking for a manner to extract the position of "*" and "+" symbols in R string.

test <- "x+y"
unlist(gregexpr("+", test))
[1] 1 2 3
unlist(gregexpr("y", test))
[1] 3

It returns the position of x or y but returns all positions for + or *.

Thank you!

since you are `unlist`ing your results, it seems that you only have one expression per line, hence use `regexpr` instead of `gregexpr`. For the case of `+` symbol, you just need to escape it as it is a metacharacter: `regexpr('\\+', test)` — Onyambu, Dec 27 '21 at 20:36
Another way to escape it is `[+]` which is a "character class" in [regex](https://stackoverflow.com/a/22944075/3358272); this is also necessary for `[*]`. Using this, you can look for *either* (not differentiating) with `[+*]`. — r2evans, Dec 27 '21 at 20:38

score 5 · Accepted Answer · answered Dec 27 '21 at 20:34

Use fixed = TRUE, by default it is FALSE and uses the regex mode where + is a metacharacter. According to ?regex

+ - The preceding item will be matched one or more times.

* - The preceding item will be matched zero or more times.

unlist(gregexpr("+", test, fixed = TRUE))
[1] 2

score 2 · Answer 2 · answered Dec 27 '21 at 21:10

2

Some other base R workarounds

> which(unlist(strsplit(test, "")) == "+")
[1] 2

> which(utf8ToInt(test) == utf8ToInt("+"))
[1] 2

answered Dec 27 '21 at 21:10

ThomasIsCoding

1

This solution appears quicker than the other one. Thank you! – POC Dec 28 '21 at 19:27

2 Answers2