Sort ArrayList of custom object and reorder in Java

Question

I have a ArrayList of CustomObject, my object is simply made of two values x and y

MyObject = (double)x && (double)y

What I want to do is:

remove duplicate from array : simply remove duplicate object and if the objects have the same x keep the one if the higher y.
reorder the list depending on the x value (x is for the time, y is a factor)

I have tried using Collections.sort to reorder my array and using a set to remove duplicate but nothing works.

Collections.sort(listPoints, new Comparator<MyObject>(){
    @Override
    public int compare(MyObject lhs, MyObject rhs) {
        return Double.compare(lhs.y, rhs.y);  
    }
});

Collections.sort(listPoints, new Comparator< MyObject >(){
    @Override
    public int compare(MyObject lhs, MyObject rhs) {
        return Double.compare(lhs.x, rhs.x);  
    }
});

What is a custom object?

Chris Martin
– Chris Martin

2014-12-24 09:24:24 +00:00
Commented Dec 24, 2014 at 9:24 — Chris Martin
– Chris Martin, Commented Dec 24, 2014 at 9:24

yole · Accepted Answer · 2014-12-24 09:27:22Z

2

Sorting a list twice with different comparators will not work. You need to compare both x and y in the same comparator.

public int compare(MyObject lhs, MyObject rhs) {
    int result = Double.compare(lhs.y, rhs.y);
    if (result != 0) return result;
    return Double.compare(lhs.x, rhs.x);
}

Using a set to remove duplicates will work if MyObject correctly implements the equals() and hashCode() methods.

edited Dec 24, 2014 at 9:27

answered Dec 24, 2014 at 9:21

yole

98k21 gold badges279 silver badges205 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

BackSlash Over a year ago

What do you mean by The sorting implemented by Collections.sort() is not stable?

yole Over a year ago

Actually please disregard that. Collections.sort() does do a stable sort, but it's irrelevant here.

user2335528 Over a year ago

than you i'll give a try

Community · Accepted Answer · 2017-05-23 12:20:33Z

0

For getting unique elements for your custom class you can just add all elements to something like HashSet. For using this you need to override the Object#hashCode() method to let it return the same hashCode() value x and y of MyObject instance. Don't forget to override Object#equals() as well.

You can refer here for more on overriding hashCode() and equals().

edited May 23, 2017 at 12:20

CommunityBot

11 silver badge

answered Dec 24, 2014 at 9:24

nitishagar

9,4313 gold badges32 silver badges41 bronze badges

1 Comment

user2335528 Over a year ago

thai you i'll give a try

Tkachuk_Evgen · Accepted Answer · 2014-12-24 09:28:34Z

0

You can implement Comparable<MyObject> in MyObject class and then use TreeSet<MyObject>, as result you have sorted unique values.

answered Dec 24, 2014 at 9:28

Tkachuk_Evgen

1,35412 silver badges17 bronze badges

Comments

SMA · Accepted Answer · 2014-12-24 09:29:18Z

0

To remove duplicates and keep the sorted order, i would suggest the following:

You store the Objects of type MyObject in a List
Sort them as you are doing with x field
iterate over the list and check for duplicates with previous elements (implements equals and hashCode methods in MyObject class) and remove one with less value in 'y' field.

answered Dec 24, 2014 at 9:29

SMA

37.2k8 gold badges53 silver badges76 bronze badges

Collectives™ on Stack Overflow

Sort ArrayList of custom object and reorder in Java

4 Answers 4

3 Comments

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related