string1 which are not in string2.
diff_two_strings is adopted from package vecsets function vsetdiff,
it returns all letters in string1 which are not in string2.Find all letters in string1 which are not in string2.
diff_two_strings is adopted from package vecsets function vsetdiff,
it returns all letters in string1 which are not in string2.
diff_two_strings(string1, string2, multiple = TRUE)A string.
A string.
A logical variable with a default of TRUE. If multiple is TRUE, it will non-unique letters, otherwise, only unique letters.