func makeHashKey(line []string, columns []int) string {
	if len(columns) == 1 {
		return line[columns[0]]
	}
	
	var key []string
	for _, v := range columns {
		key = append(key, line[v])
	}
	
	return strings.Join(key, ",")
}
// makeHashKey concats columns to make a hash key
makeHashKey concats columns to make a hash key
// makeHashKey concats columns to make a hash key
func makeHashKey(line []string, columns []int) string {
	if len(columns) == 1 {
		return line[columns[0]]
	}
	var key []string
	for _, v := range columns {
		key = append(key, line[v])
	}
	return strings.Join(key, ",")
}
func makeHashKey ( line [ ] string , columns [ ] int ) string { if len ( columns ) == 1 { return line [ columns [ 0 ] ] } var key [ ] string for _ , v := range columns { key = append ( key , line [ v ] ) } return strings . Join ( key , " " ) }
makeHashKey concats columns to make a hash key
makeHashKey concats columns to make a hash key