Getting max value from an arraylist of objects?

Question

Is there an easy way to get the max value from one field of an object in an arraylist of objects? For example, out of the following object, I was hoping to get the highest value for the Value field.

Example arraylist I want to get the max value for ValuePairs.mValue from.

ArrayList<ValuePairs> ourValues = new ArrayList<>();
outValues.add(new ValuePairs("descr1", 20.00));
outValues.add(new ValuePairs("descr2", 40.00));
outValues.add(new ValuePairs("descr3", 50.00));

Class to create objects stored in arraylist:

public class ValuePairs {

    public String mDescr;
    public double mValue;

    public ValuePairs(String strDescr, double dValue) {
        this.mDescr = strDescr;
        this.mValue = dValue;
    }
}

I'm trying to get the max value for mValue by doing something like (which I know is incorrect):

double dMax = Collections.max(ourValues.dValue);

dMax should be 50.00.

score 24 · Accepted Answer · edited May 23 '17 at 12:09

24

Use a Comparator with Collections.max() to let it know which is greater in comparison.

Also See

How to use custom Comparator

edited May 23 '17 at 12:09

Community

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answered Oct 12 '13 at 20:09

jmj

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M. Schena · Answer 2 · 2021-09-15T06:42:06.983

23

With Java 8 you can use stream() together with it's predefined max() function and Comparator.comparing() functionality with lambda expression:

ValuePairs maxValue = values.stream().max(Comparator.comparing(v -> v.getMValue())).get();

Instead of using a lambda expression, you can also use the method reference directly:

ValuePairs maxValue = values.stream().max(Comparator.comparing(ValuePairs::getMValue)).get();

edited Sep 15 '21 at 06:42

answered Nov 22 '17 at 08:29

M. Schena

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1

Is there a way to get *all* the `ValuePairs` matching the `.max()`? – Nato Boram Aug 08 '19 at 23:59
That would be something like this after you have found out the max value: `List maxValues = ourValues.stream().filter(v -> v.mValue == maxValue.mValue).collect(Collectors.toList());` – M. Schena Aug 09 '19 at 07:07

score 9 · Answer 3 · answered Dec 20 '15 at 13:47

This has been answered multiple time already, but since it's the first result on google I will give a Java 8 answer with an example.

Take a look at the stream feature. Then you can get the max form an List of Objects like this:

List<ValuePairs> ourValues = new ArrayList<>();

ourValues.stream().max(comparing(ValuePairs::getMValue)).get()

By the way in your example, the attributes should be private. You can then access them with a getter.

score 1 · Answer 4 · answered Oct 12 '13 at 20:09

1

You should iterate over the list comparing/finding the max value O(N). If you need to do this often replace the list with a PriorityQueue O(1) to find the max.

answered Oct 12 '13 at 20:09

Cratylus

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score 0 · Answer 5 · answered May 12 '20 at 06:28

Here fist and last is intervals between two indexes of arraylist you can also get for a complete list by removing them and i=0 upto size of float list.

// for min value

public String getMinValue(ArrayList list, int first, int last) {

        List<Float> floatList = new ArrayList<>();

        for (int i = 0; i < list.size(); i++) {
            Float prova2 = ((Double) list.get(i)).floatValue();
            floatList.add(prova2);
        }
        float min = Float.MAX_VALUE;
        String minValue = "";

        for (int i = first; i < last; i++) {


            if (floatList.get(i) < min) {
                min = floatList.get(i);
            }
        }
        minValue = String.format("%.1f", min);
        return minValue;
    }

// for max value

    public String getMaxValue(List<Object> list, int first, int last) {

        List<Float> floatList = new ArrayList<>();

        for (int i = 0; i < list.size(); i++) {
            Float prova2 = ((Double) list.get(i)).floatValue();
            floatList.add(prova2);
        }

        float max = Float.MIN_VALUE;
        String maxValue = "";

        for (int i = first; i < last; i++) {


            if (floatList.get(i) > max) {
                max = floatList.get(i);
            }
        }
        maxValue = String.format("%.1f", max);
        return maxValue;
    }

Getting max value from an arraylist of objects?

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