public static Map ordinalMap(Iterator tuples,String field){
  return ordinalMap(tuples,field,DefaultLiteralComparator.getInstance());
}

public static Map ordinalMap ( Iterator tuples , String field ) { return ordinalMap ( tuples , field , DefaultLiteralComparator . getInstance ( ) ) ; }
get map mapping from column values ( as object instances ) to their ordinal index in a sorted array .
