Extract text before or after nth occurrence of pattern.

Extract the part of a string which is before or after the nth occurrence of a specified pattern, vectorized over the string.

str_after_nth(string, pattern, n)

str_after_first(string, pattern)

str_after_last(string, pattern)

str_before_nth(string, pattern, n)

str_before_first(string, pattern)

str_before_last(string, pattern)

Arguments

string

A character vector.

pattern

The pattern to look for.

The default interpretation is a regular expression, as described in stringi::about_search_regex.

To match a without regular expression (i.e. as a human would), use coll(). For details see stringr::regex().

n

A vector of integerish values. Must be either length 1 or have length equal to the length of string. Negative indices count from the back: while n = 1 and n = 2 correspond to first and second, n = -1 and n = -2 correspond to last and second-last. n = 0 will return NA.

Value

A character vector.

Details

• str_after_first(...) is just str_after_nth(..., n = 1).

• str_after_last(...) is just str_after_nth(..., n = -1).

• str_before_first(...) is just str_before_nth(..., n = 1).

• str_before_last(...) is just str_before_nth(..., n = -1).

See also

Other bisectors: str_before_last_dot()

Examples

string <- "abxxcdxxdexxfgxxh"
str_after_nth(string, "xx", 3)
#> [1] "fgxxh"
str_before_nth(string, "e", 1:2)
#> [1] "abxxcdxxd" NA         
str_before_nth(string, "xx", -3)
#> [1] "abxxcd"
str_before_nth(string, ".", -3)
#> [1] "abxxcdxxdexxfg"
str_before_nth(rep(string, 2), "..x", -3)
#> [1] "abxx" "abxx"
str_before_first(string, "d")
#> [1] "abxxc"
str_before_last(string, "x")
#> [1] "abxxcdxxdexxfgx"
string <- c("abc", "xyz.zyx")
str_after_first(string, ".") # using regex
#> [1] "bc"     "yz.zyx"
str_after_first(string, coll(".")) # using human matching
#> [1] NA    "zyx"
str_after_last(c("xy", "xz"), "x")
#> [1] "y" "z"