Remove duplicates items from arraylist and hashmap

问题

I have an arraylist with the name of who pay something, and another arraylist with the cost of each payment. For example:

nameArray = Nicola, Raul, Lorenzo, Raul, Raul, Lorenzo, Nicola
priceArray = 24, 12, 22, 18, 5, 8, 1

I need to sum the cost of each person. So the array must become:

nameArray = Nicola, Raul, Lorenzo
price Array = 25, 35, 30

And then, ordering the array by price, so:
nameArray = Raul, Lorenzo, Nicola
priceArray = 35, 30, 25

I'm using a Map, but the problem now is that I see multiple times the name of each person and each payment with the sum. That's the code:

public void bubble_sort(ArrayList<String> nameArray, ArrayList<BigDecimal> priceArray) {
    Map<String, BigDecimal> totals = new HashMap<>();

    for (int i = 0; i < nameArray.size(); ++i) {
        String name = nameArray.get(i);
        BigDecimal price = priceArray.get(i);

        BigDecimal total = totals.get(name);

        if (total != null) {
            totals.put(name, total.add(price));
        } else {
            totals.put(name, price);
        }
    }
    for (Map.Entry<String, BigDecimal> entry : totals.entrySet()) {
        nameArray.add(entry.getKey());
        priceArray.add(entry.getValue());
    }

    for (int i = 0; i < priceArray.size(); i++) {
        for (int j = 0; j < priceArray.size() - 1; j++) {
            if (priceArray.get(j).compareTo(priceArray.get(j + 1)) < 0) {
                BigDecimal tempPrice = priceArray.get(j);
                String tempName = nameArray.get(j);
                priceArray.set(j, priceArray.get(j + 1));
                nameArray.set(j, nameArray.get(j + 1));
                priceArray.set(j + 1, tempPrice);
                nameArray.set(j + 1, tempName);
            }

        }

    }
    Log.v("New nameArray", nameArray.toString());
    Log.v("New priceArray", priceArray.toString());

}

That's the output of the log:

New nameArray: [Nico, Nico, Raul, Nico, Raul, Lorenzo, Lorenzo, Raul]
New priceArray: [43.50, 25.50, 18.98, 18.00, 16.98, 9.50, 9.50, 2.00]

Nico paid 18.00 + 25.50 = 43.50, Raul 16.98 +2 = 18.98 and lorenzo 9.50. The name and the price were insert by the user dinamically.

I need to display the array like this:

nameArray: Nico, Raul, Lorenzo
priceArray: 43.50, 16.98, 9.50

回答1:

You are adding the entries of the Map to the original Lists. You should clear them first:

nameArray.clear();
priceArray.clear();
for (Map.Entry<String, BigDecimal> entry : totals.entrySet()) {
    nameArray.add(entry.getKey());
    priceArray.add(entry.getValue());
}

Or, if you don't want to overwrite the original Lists, you should create new ArrayLists.

回答2:

The easiest way is to implement a Set<String> as a LinkedHashSet<String>() to preserve insert order. This will insure uniqueness in your set.

Sets check hashCode() and the accompanying equals(). Items are considered to be equal if their hashCode() are their same.

If you implement your own class you can override hashCode() and equals() to check for uniqueness as well.

来源：https://stackoverflow.com/questions/53706649/remove-duplicates-items-from-arraylist-and-hashmap

标签

java

android

arraylist

hashmap