printing random array variable only once in java

Question

I have an assignment for uni where I have to create a Java program that produces a random pairing customers and their transaction totals.

It comes in two parts where the first part produces the customers and their transactions like so:

Customer ID, Transaction Value
1, 74.36 
1, 44.98 
3, 6.44
0, 19.13
3, 59.44
2, 81.56
0, 87.21
4, 40.9
1, 42.11
3, 66.05

the second summarises the total number of transactions for each customer like so:

Customer: 1 Transactions: 3.0
Customer: 1 Transactions: 3.0
Customer: 3 Transactions: 3.0
Customer: 0 Transactions: 2.0
Customer: 3 Transactions: 3.0
Customer: 2 Transactions: 1.0
Customer: 0 Transactions: 2.0
Customer: 4 Transactions: 1.0
Customer: 1 Transactions: 3.0
Customer: 3 Transactions: 3.0

My problem is the second section should only produce each customer ID once ie 1,3,0,2,4 . I can only do this using int and double variables and without creating any other arrays or structures. My code can be found below.

 import java.util.*;

 public class Assignment3 {
   public static long studentNumber=1234567; 

   public static int customerID[];
   public static double transactionValue[];

   public static void initialiseData(int size) {
     customerID = new int[size];
     transactionValue = new double[size];

     Random rand = new Random(studentNumber);
     for (int i=0; i<size; i++) {
       customerID[i] = rand.nextInt(size / 2);
       transactionValue[i] = rand.nextInt(10000) / 100.0;
     }
   }

   public static void main(String args[]) {
     int size=10;

    initialiseData(size);

    // Your code should only be below this line
    double transaction = 0;
    int customer = 0;
    int customer_Total = 0;
    int count = 0;
    int customer_count = 0;
    double transaction_Total = 0;

    System.out.println("Customer ID, Transaction Value");

    for (size= 0; size < customerID.length; size++) {
    customer= customerID[size];
    transaction= transactionValue[size];
    System.out.println(customer + ", " + transaction);

    }

    System.out.println("");

    for(customer_count = 0; customer_count < customerID.length; customer_count++) {
      transaction_Total= 0;
      customer_Total = customerID[customer_count];
      count = customerID[customer_count];
      //System.out.println(count);

      for (int customer_count2 = 0;
           customer_count2 < customerID.length;
           customer_count2++) {                         
        if (customer_Total == customerID[customer_count2]) {
          transaction_Total++;

          //System.out.println(customer_count2);
        }
      }

      System.out.println("Customer: "+ customer_Total + " " +
                         "Transactions: " + transaction_Total); 
    }

    // Your code should not be below this line

  }
}

Answer 1

I suggest you look at how Collections.shuffle works. In your case you can create an array of all possible values and "shuffle" then in a random order.

Answer 2

EDIT: in this code:

for(customer_count = 0; customer_count < customerID.length; customer_count++) {
  transaction_Total= 0;
  customer_Total = customerID[customer_count];
  count = customerID[customer_count];
  //System.out.println(count);

  for (int customer_count2 = 0;
       customer_count2 < customerID.length;
       customer_count2++) {                         
    if (customer_Total == customerID[customer_count2]) {
      transaction_Total++;

      //System.out.println(customer_count2);
    }
  }

  System.out.println("Customer: "+ customer_Total + " " +
                     "Transactions: " + transaction_Total); 
}

add the following after 'transaction_Total= 0;':

int wasBefore = 0; //are you allowed to use boolean variables?
for (int customer_count3 = 0;
       customer_count3 < customer_count;
       customer_count3++) {                         
    if (customer_Total == customerID[customer_count3]) {
      wasBefore = 1;
    }
}
if (wasBefore==1) {continue;}

In this way you still get random order of customers without repreating them

Answer 3

so your homework is a little bit irritating, since it is unusual to make such a restriction as don't use arrays.

But you could do the following: Your customer ids go from 0 to size/2 so it is possible to write a loop which counts the transactions for every possible customer. Like this

for(int customer_id = 0; customer_id <= size /2 ; customer_id++){
    int transaction_sum = 0;
    for (j= 0; j < customerID.length; j++)
        if(customerID[j] == i)
             transaction_sum++;
    if( transaction_sum > 0)
        System.out.println("Customer: " + customer_id +
                           "  Transactions: " + transaction_sum);
}

but this is not a nice solution, beacuse this is slow for large number of possible ids.