Determine birth year from CPR-nummer (Danish personal identifier)

cpr-to-year.groovy

def cpr = '0101374000'

def match = (cpr =~ /^\d{4}(\d{\d}2})(\d)\d{3}$/)[0]

def year = match[1] as Integer
def x = match[2] as Integer

switch (x) {
  case 0..3: year += 1900; break;
  case [4, 9]: year += year <= 36 ? 2000 : 1900; break;
  case 5..8: year += year <= 57 ? 2000 : 1800; break;
}