why when use groupBy(2).sortGroup(0, Order.DESCENDING); not group by and not sort

[hagersaleh]

why when use groupBy(2).sortGroup(0, Order.DESCENDING); not group by and not
sort

I want sort DataSet How can I do that?

customers = customers.filter(
            new FilterFunction<Customer>() {
                    @Override
                    public boolean filter(Customer c) {
                    
                   
                        return    
Integer.parseInt(c.getField(0).toString())<=5 ;
                         
                    }
            }); 
       
       customers.groupBy(2).sortGroup(0, Order.DESCENDING);
       System.out.println(customers.print()); 
       customers.writeAsCsv("/home/hadoop/Desktop/Dataset/output.csv", "\n",
"|");
       env.execute();  


public static class Customer extends
Tuple5<Long,String,String,String,String> {
                
        }
        private static DataSet<Customer>
getCustomerDataSet(ExecutionEnvironment env) {
                return 
env.readCsvFile("/home/hadoop/Desktop/Dataset/customer.csv")
                                        .fieldDelimiter('|')
                                       
.includeFields("11100110").ignoreFirstLine()
                                        .tupleType(Customer.class);
        }

the result not sort
2> (1,Customer#000000001,IVhzIApeRb ot&&c&&E,711.56,BUILDING)
2> (2,Customer#000000002,XSTf4&&NCwDVaWNe6tEgvwfmRchLXak,121.65,AUTOMOBILE)
2> (3,Customer#000000003,MG9kdTD2WBHm,7498.12,AUTOMOBILE)
2> (4,Customer#000000004,XxVSJsLAGtn,2866.83,MACHINERY)
2> (5,Customer#000000005,KvpyuHCplrB84WgAiGV6sYpZq7Tj,794.47,HOUSEHOLD)



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