code: public static List<String> readUniqueColumnValuesFromDelimitedFile(String filename, 
        int columnNumber, String delimiter) {
      Set<String> values = Sets.newHashSet(
          readColumnFromDelimitedFile(filename, columnNumber, delimiter));
      return Lists.newArrayList(values);
    }
docs: Returns a list of the unique values in {@code columnNumber} of
  {@code filename}. The columns of {@code filename} are delimited
  by {@code delimiter}.
  
  @param filename
  @param columnNumber
  @param delimiter
  @return