Often, we want the part of a string that comes before or after a given pattern.
str_before_nth() gives you the part of a string before
the nth appearance of a pattern. It has the
friends str_before_first() and
str_before_last().
string <- "ab..cd..de..fg..h"
str_before_first(string, "e")
#> [1] "ab..cd..d"
str_before_nth(string, "\\.", 3)
#> [1] "ab..cd"
str_before_last(string, "\\.")
#> [1] "ab..cd..de..fg."
str_before_nth(string, ".", -3)
#> [1] "ab..cd..de..fg"
str_before_nth(rep(string, 2), fixed("."), -3)
#> [1] "ab..cd..de." "ab..cd..de."str_after_nth() gives you the part of a string after the
nth appearance of a pattern. It has the friends
str_after_first() and str_after_last().
Let’s write a function to figure out which task each of the lads did.
library(magrittr)
get_task <- function(string, name) {
str_c(name, " did the ") %>%
str_after_first(string, .) %>%
str_before_first("[\\.,]")
}
get_task(string, "James")
#> [1] "cooking"
get_task(string, "Harry")
#> [1] "cleaning"get_task() would have been more difficult to write
without str_after_first() and
str_before_first().