str_sub(string, start = 1L, end = -1L, omit_na = FALSE) <- value 1. shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2") str_sub(shopping_list,1,3) <- "AAA" # 结果 [1] "AAAles x4" "AAA of flour" "AAA of sugar" "AAAk x2" str_sub(s...