How to sort object using a multi map?

Question

Hi I'm trying to sort an object based on a value of that object. Originally I used TreeMap which did the sorting but there were some non-unique keys which were removed so that didn't work. I googled around and came across Guava MultiMap. But how do I actually use this to sort the values?

Basically I'm trying to sort budget information based on the diffYTD_percentage value. Thanks!

Multimap<Double, BudgetInformation> multiMap = ArrayListMultimap.create();
    for (Budget budget : budgets) {
        BudgetInformation budgetInfo = getBudget(budget.getId());
        double actualToDate = budgetInfo.getActualToDate();
        double budgetToDate = budgetInfo.getTotalBudgetToDate();
        double diffYTD_value = budgetToDate - actualToDate;
        double diffYTD_percentage_value = 0.0;
        if (budgetToDate != 0.0) {
            double fraction = actualToDate / budgetToDate;
            fraction = fraction - 1;
            diffYTD_percentage_value = fraction * 100;
        }
        multiMap.put(diffYTD_percentage_value, budgetInfo);
    }

    Iterator<BudgetInformation> budgetIterator = multiMap.values().iterator();

score 3 · Accepted Answer · answered Sep 24 '14 at 12:10

Using Tree in order to sort collection is wrong approach. In Java there are dedicated utility methods to sort list, Collections.sort(List<T extends Comparable<? super T>> list) and Collections.sort(List<T> list, Comparator<? super T> c). The first is used to sort list where elements have natural ordering (basically implement Comparable interface), the later is used in cases like your own, when you need to sort elements using custom ordering.

So, basically what you need to do is to create Comparator that will compare two BusinessInfo instances based on diffYTD_percentage_value and call Collections.sort with this comparator.

    Comparator<BudgetInformation> budgetInfoCmp = new Comparator<BudgetInformation>() {
        private double getDiffYTDPercentage(BudgetInformation budgetInfo) {
            double actualToDate = budgetInfo.getActualToDate();
            double budgetToDate = budgetInfo.getTotalBudgetToDate();
            double diffYTDValue = budgetToDate - actualToDate;
            double diffYTDPercentageValue = 0.0;
            if (budgetToDate != 0.0) {
                double fraction = actualToDate / budgetToDate;
                fraction = fraction - 1;
                diffYTDPercentageValue = fraction * 100;
            }
            return diffYTDPercentageValue;
        }

        @Override
        public int compare(BudgetInformation o1, BudgetInformation o2) {
            return Double.compare(getDiffYTDPercentage(o1), getDiffYTDPercentage(o2));
        }
    };

    List<BudgetInformation> budgetInformationsToSort = getBudgetInformations();
    Collections.sort(budgetInformationsToSort, budgetInfoCmp);

Also try to avoid using underscore in variable naming, as under Java naming convention variable names should be in camel case.

Abhiroop Sarkar · Answer 2 · 2014-09-24T10:52:21.470

0

How about using TreeMultiMap? It doesnt support duplicate key-value pair. But duplicate keys are fine.

edited Sep 24 '14 at 10:52

answered Sep 24 '14 at 10:44

Abhiroop Sarkar

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It won't let me put Class BudgetInformation into a TreeMultiMap. TreeMultiMap does not work. – OneTwo Sep 24 '14 at 10:52
If you open that link you will find it says `Class TreeMultimap` The key and value are generics. It can be double,long etc. – Abhiroop Sarkar Sep 24 '14 at 10:59
SO how can I then use it to sort BudgetInformation? – OneTwo Sep 24 '14 at 11:05
use the same `put` statement that you are using in your code snippet. It will internally order it by keys. – Abhiroop Sarkar Sep 24 '14 at 11:07
But what do I put in the TreeMultimap ? – OneTwo Sep 24 '14 at 11:09
the exact same code that you wrote in your code snippet `put(diffYTD_percentage_value, budgetInfo);` – Abhiroop Sarkar Sep 24 '14 at 11:12
I get incompatible types no instances of type variables so that TreeMultimap conforms to TreeMultiMap – OneTwo Sep 24 '14 at 11:15
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/61833/discussion-between-abhiroop-sarkar-and-fionn). – Abhiroop Sarkar Sep 24 '14 at 11:17

How to sort object using a multi map?

2 Answers2