library(stringr)
from <- c("Valid from", "Zipcode from", "0000AA", "1798AA", "8900AA", "9167aa")
to <- c("Valid from", "Zipcode to", "1797zz", "8899ZZ", "9166ZZ", "9999ZZ")
str_detect(from, "^\\d{4}[A-Za-z]{2}$")
from[str_detect(from, "^\\d{4}[A-Za-z]{2}$")]
str_detect(to, "^\\d{4}[A-Za-z]{2}$")
to[str_detect(to, "^\\d{4}[A-Za-z]{2}$")]
bGlicmFyeShzdHJpbmdyKQpmcm9tIDwtIGMoIlZhbGlkIGZyb20iLCAiWmlwY29kZSBmcm9tIiwgIjAwMDBBQSIsICIxNzk4QUEiLCAiODkwMEFBIiwgIjkxNjdhYSIpCnRvIDwtIGMoIlZhbGlkIGZyb20iLCAiWmlwY29kZSB0byIsICIxNzk3enoiLCAiODg5OVpaIiwgIjkxNjZaWiIsICI5OTk5WloiKQpzdHJfZGV0ZWN0KGZyb20sICJeXFxkezR9W0EtWmEtel17Mn0kIikKZnJvbVtzdHJfZGV0ZWN0KGZyb20sICJeXFxkezR9W0EtWmEtel17Mn0kIildCgpzdHJfZGV0ZWN0KHRvLCAiXlxcZHs0fVtBLVphLXpdezJ9JCIpCnRvW3N0cl9kZXRlY3QodG8sICJeXFxkezR9W0EtWmEtel17Mn0kIild