Tests the levels of x contain any instances of "Don't know".  If so, replaces these levels with NA
remove_dont_know(x, dk = "Don't Know")Character vector or factor
Character vector, containing search terms, e.g. c("Don't know", "Don't Know")
A factor with "Dont know" removed
Other Functions to clean data: encToInt,
  fix_common_encoding_problems,
  fix_levels_01_spss,
  has_dont_know, intToEnc,
  leveltest,
  remove_all_dont_know