Sort array as ascending

Question

So i have HashMap which i convert it to Object so i can sort it by value, now by default i sort it as descending, but i would need other option too to sort it as ascending.

I used simple array sort:

HashMap<String, Integer> prefMap = getMyList();

Object[] a = prefMap.entrySet().toArray();

Arrays.sort(a, new Comparator() {
    public int compare(Object o1, Object o2) {
        return ((Map.Entry<String, Integer>) o2).getValue()
                .compareTo(((Map.Entry<String, Integer>) o1).getValue());0
    }
});

The upper code works for descending, should i just compare with if/else if i want to sort them as ascending?

If you are working with Java 8+, use `lambda` or `method reference`. — 6324, Jun 21 '18 at 14:09
And please: avoid using **raw** types. That should be a `Comparator`, then you wouldnt need to use Object inside! — GhostCat, Jun 21 '18 at 14:10
@GhostCat you probably meant `Comparator>` OP's sorting an array created from the entry set — Lino, Jun 21 '18 at 14:13
See this https://stackoverflow.com/a/1946723/1531124 answer from the duplicated question for example. — GhostCat, Jun 21 '18 at 14:14

Arnaud · Answer 1 · 2018-06-21T14:20:41.563

1

To sort ascending, you may simply call the reversed version of your Comparator :

Arrays.sort(a, new Comparator<Map.Entry<String, Integer>>() {

    public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
        return (o2).getValue().compareTo((o1).getValue());
    }

}.reversed()); // <-- see here

edited Jun 21 '18 at 14:20

answered Jun 21 '18 at 14:11

Arnaud

17,229
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Same here: please dont copy code blindly - consider fixing the raw type usage. – GhostCat Jun 21 '18 at 14:14

score 0 · Answer 2 · answered Jun 21 '18 at 14:10

0

Swap o2 and o1 in compareTo, you get it ascending....

HashMap<String, Integer> prefMap = getMyList();    
Object[] a = prefMap.entrySet().toArray();   
Arrays.sort(a, new Comparator() {
    public int compare(Object o1, Object o2) {
        return ((Map.Entry<String, Integer>) o1).getValue()
                .compareTo(((Map.Entry<String, Integer>) o2).getValue());
    }
});

answered Jun 21 '18 at 14:10

Ying Cherry

143
1
5

2

Sigh. Instead of just copying that code, at least go in and drop the *raw* type usage. – GhostCat Jun 21 '18 at 14:11

Sort array as ascending

2 Answers2