Get indices of all character elements matches in string in R

问题

I want to get indices of all occurences of character elements in some word. Assume these character elements I look for are: l, e, a, z.

I tried the following regex in grep function and tens of its modifications, but I keep receiving not what I want.

grep("/([leazoscnz]{1})/", "ylaf", value = F)

gives me

numeric(0)

where I would like:

[1] 2 3 

回答1:

To use grep work with individual characters of a string, you first need to split the string into separate character vectors. You can use strsplit for this:

strsplit("ylaf", split="")[[1]]
[1] "y" "l" "a" "f"

Next you need to simplify your regular expression, and try the grep again:

strsplit("ylaf", split="")[[1]]
grep("[leazoscnz]", strsplit("ylaf", split="")[[1]])

[1] 2 3

---

But it is easier to use gregexpr:

gregexpr("[leazoscnz]", "ylaf")
[[1]]
[1] 2 3
attr(,"match.length")
[1] 1 1
attr(,"useBytes")
[1] TRUE

来源：https://stackoverflow.com/questions/24508413/get-indices-of-all-character-elements-matches-in-string-in-r