Select an object on the basis of its minimum attribute value from list in Java

Question

I have a class

public class LocationDistances {
    String locs;
    double distances;

}

and an ArrayList composed of LocationDistances objects in another class

ArrayList<LocationDistances> locsDis = new ArrayList(Arrays.asList(
    new LocatoinDistances("abc",23.234556),
    new LocatoinDistances("xyz",3.3444566),
    . . . 
    . . .
    . . .

));

How to select LocationDistances.locs from Array list on the basis of minimum value of LocationDistances.distance from the locsDis arrayList?

You can override equals and hashcode methods of Object class. Or you can write a Comparator to sort your list with minimum distance on top so you can retrieve it as first element in your list. — Mandar Pandit
– Mandar Pandit, Commented Apr 17, 2015 at 4:29

David Limkys · Accepted Answer · 2015-04-17 04:54:18Z

7

If you are using Java 8 (You should :)) :

locsDis.stream().min((first, second) -> Double.compare(first.distance, second.distance)).get();

Edit: Decided to make this post a bit more comprehensive to help those of us that are still confined to Java < 8 but can use the awesome library guava :)

Java 6 & 7 With guava (Google util library):

Ordering<LocationDistances> ordering = new Ordering<LocationDistances>() {
    @Override
    public int compare(LocationDistances left, LocationDistances right) {
        return Double.compare(left.distance, right.distance);
    }
};
return ordering.max(list);

edited Apr 17, 2015 at 4:54

answered Apr 17, 2015 at 4:28

David Limkys

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Comments

prasadmadanayake · Accepted Answer · 2015-04-17 04:38:20Z

5

Something like this would work if there are no duplicate distances.

LocationDistances min=null;
for(LocationDistances x:locsDis){
    min=(min==null||x.distances<min.distances)?x:min;
}
String minimumDistance=min.locs;

if there are duplicate distances use something like this

ArrayList<LocationDistances> min=new  ArrayList<LocationDistances>();

for(LocationDistances x:locsDis){
    if(min.size()==0||x.distances==min.get(0).distances)
           min.add(x);
    else if(x.distances<min.get(0).distances){
           min.clear();
           min.add(x);
    }               
}

answered Apr 17, 2015 at 4:38

prasadmadanayake

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Comments

Slow Trout · Accepted Answer · 2015-04-17 04:47:10Z

1

Use a Priority Queue with a custom Comparator. (Use poll/peek for the minimum value)

public class MyComparator implements Comparator<LocationDistance>
{
  @Override
  public int compare(LocationDistance ld1, LocationDistance ld2)
  {
    return  Double.compare(ld1.distances, ld2.distances);
   }
}
......
......
PriorityQueue collection = new PriorityQueue<LocationDistance>(5, new MyComparator());

edited Apr 17, 2015 at 4:47

answered Apr 17, 2015 at 4:31

Slow Trout

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Comments

Anantha Sharma · Accepted Answer · 2015-04-17 04:30:36Z

0

@David Limkys is right, that would be a solution in Java 8, for java 6 & 7 the follwing would do.

public class MainCLass {

    /**
     * 
     */
    public MainCLass() {
        // TODO Auto-generated constructor stub
    }

    public static void main(String[] args) {

        LocationDistances[] arr = new LocationDistances[] {
                new LocationDistances("abc", 23.234556),
                new LocationDistances("xyz", 3.3444566), };

        ArrayList<LocationDistances> locsDis = new ArrayList(Arrays.asList(arr));

        Collections.sort(locsDis, new Comparator<LocationDistances>() {
            public int compare(LocationDistances o1, LocationDistances o2) {
                return (int)( o1.distances - o2.distances);
            }
        });

    }

}

class LocationDistances {
    String locs;
    double distances;

    /**
     * @param locs
     * @param distances
     */
    public LocationDistances(String locs, double distances) {
        super();
        this.locs = locs;
        this.distances = distances;
    }

    @Override
    public String toString() {
        return String.format("LocationDistances [locs=%s, distances=%s]", locs,
                distances);
    }

}

answered Apr 17, 2015 at 4:30

Anantha Sharma

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2 Comments

Paul Boddington Over a year ago

return (int)( o1.distances - o2.distances); does not work. You could end up rounding the difference to zero when the two original doubles were not equal.

Anantha Sharma Over a year ago

true, alternatively, we could compare them and return 0,1,-1 but i guess i was lazy :)

pabloapa · Accepted Answer · 2015-04-17 04:30:50Z

You could implement Comparable on LocationDistances and sort the ArrayList using the comparator for the distance in ascending order.

public class LocationDistances implements Comparable {
    String locs;
    double distances;

    @Override
    public int compareTo(LocationDistances anotherLocation) {
        double otherLocDistances = ((LocationDistances)anotherLocation).getDistances();

        /* ascending order */
        return this.distances - otherLocDistance;

        /* descending order */
        //return otherLocDistance - this.distances;
    }
}

And then call:

ArrayList<LocationDistances> locsDis = new ArrayList(Arrays.asList(
    new LocationDistances("abc",23.234556),
    new LocationDistances("xyz",3.3444566),
    . . . 
    . . .
    . . .

));
Collections.sort(locsDis);

Prashant G · Accepted Answer · 2015-04-17 04:37:16Z

This is what your are looking for:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;


public class Run {
    public static void main(String[]args){
        ArrayList<LocationDistances> locsDis = new ArrayList(Arrays.asList(
                new LocationDistances("abc",23.234556),
                new LocationDistances("xyz",3.3444566)));

        ArrayList<Double> distances = new ArrayList<Double>();
        for (LocationDistances locationDistances : locsDis) {
            distances.add(locationDistances.getDistances());
        }
        double minimum = Collections.min(distances);
        System.out.println(minimum);
    }
}

class LocationDistances  {

    public LocationDistances(String locs, double distances) {
        this.locs = locs;
        this.distances = distances;
    }
    String locs;
    double distances;
    public String getLocs() {
        return locs;
    }
    public void setLocs(String locs) {
        this.locs = locs;
    }
    public double getDistances() {
        return distances;
    }
    public void setDistances(double distances) {
        this.distances = distances;
    }

}

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