'How to iterate through ArrayList<Double> values of HashMap?

A question from a total newbie. Sorry.

I have this customersOrders HashMap that takes String as keys and ArrayList<Double> as values. I need to find the total sum of orders for each customer and the maximum total sum in order to find the biggest customer. How do I manage to do that using just nested For loops and HashMap methods? I'm totally stuck on that.

public class Test {

    public static void main(String[] args) {

        HashMap<String, ArrayList<Double>> customersOrders;

        customersOrders = new HashMap<>();
        ArrayList<Double> orders = new ArrayList<>();
        orders.add(55.50);
        orders.add(78.30);
        orders.add(124.75);
        customersOrders.put("John", orders);

        orders = new ArrayList<>();
        orders.add(28.35);
        orders.add(37.40);
        customersOrders.put("Helen", orders);

        orders = new ArrayList<>();
        orders.add(150.10);
        customersOrders.put("Thomas", orders);

        orders = new ArrayList<>();
        orders.add(230.45);
        orders.add(347.20);
        customersOrders.put("Robert", orders);

        orders = new ArrayList<>();
        orders.add(530.25);
        orders.add(325.40);
        orders.add(11550.70);
        orders.add(2480.65);
        customersOrders.put("Jennifer", orders);

        System.out.println(customersOrders);

    }
}

So far I've been trying to do something like this but obviously with no success:

double maxOrder = 0;
String customerName = "";

for (ArrayList<Double> orders : customersOrders.values()) {
    for (double orderPrice : orders) {
        if (orderPrice > maxOrder) {
            maxOrder = orderPrice;
        }
    }
}
        
for (String name : customersOrders.keySet()) {
    if (maxOrder.equals(customersOrders.get(name))) {
        customerName = name;
        break;
    }
}
javaarraylisthashmap


Solution 1:[1]

Maybe something like this:

        Map<String, Double> customersSum = new HashMap<>();
        Double maxSum = Double.MIN_VALUE;
        String customerWithMaxSum;
        
        for (Map.Entry<String, List<Double>> entry: customersOrders.entrySet()) {
            String customerId = entry.getKey();
            List<Double> customerOrders = entry.getValue();
            
            Double customerSum = customerOrders.stream().mapToDouble(d -> d).sum();
            customersSum.put(customerId, customerSum);
            
            if (customerSum > maxSum) {
                maxSum =  customerSum;
                customerWithMaxSum = customerId;
            }
        }

Also could use stream pi for the second part:

Optional<String> customerWithMaxSum = customersSum.entrySet()
                .stream()
                .max(Comparator.comparingDouble(Map.Entry::getValue))
                .map(Map.Entry::getKey);

Solution 2:[2]

Your logic code is not correct

    for (double orderPrice : orders) {
        if (orderPrice > maxOrder) {
            maxOrder = orderPrice;
        }
    }

You are not adding the prices then comparing with maxOrder you instead compare each price with maxOrder. this is not what was required in your question.

You should do this instead

    double ordersSum = 0;
    for (double orderPrice : orders) {
        ordersSum += orderPrice;
    }
    if (ordersSum > maxOrder) {
        maxOrder = ordersSum;
    }

and in your second for loop, you are comparing a double value with an arraylist which should result a compilation error you should compare the sum for products from each custom to maxOrder.

I should note here that this code is not very efficient you can instead loop on keys as you did in the second loop then calculate the sum inside of it and compare to maxOrder I will leave this implementation as an exercise for you.

Solution 3:[3]

You are iterating over the values in the orders Map. This doesn't tell you who that is associated with. Instead, you could iterate over the keyset or entryset, calculate the sum for that customer, and compare this to a running maximum. Since you specified using for-loops, the following excludes use of the Stream API.

String maxOrderCustomer = null;
double maxOrder = 0.0;
for (Map.EntrySet<String,List<Double>> entry : customerOrders.entrySet()) {
  Double sum = 0.0;
  for (Double order : entry.getValue();
    sum += order;
  }
  if (order > maxOrder) {
    maxOrder = order;
    maxOrderCustomer = entry.getKey();
  }
}

At this point, you will have the name of the customer with the largest sum and that sum value. If you want to display the relevant list of orders, you can use the name to pull the list from the original Map.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1
Solution 2 Abdullah Khaled
Solution 3 vsfDawg

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