How to get index of multiple maximum value in List

Question

In given list of Integers i want to find the multiple index of maximum value in List.

For example,

List<Integer> len=Arrays.asList(9,3,6,5,4,9);

Now i want to find the largest element which is 9 and its all index which are 0 and 5.

i have tried following code but it only gives me the first occurrence of element so from this code i am getting output only 0 not 5.

IntStream.range(0,len.size()).reduce((a, b) -> len.get(a) < len.get(b)?b:a).ifPresent(ix -> System.out.println("Index -"+ix));

So how can i achieve that ?

Andrei G · Accepted Answer · 2017-02-24 08:39:33Z

3

Something like this:

int max = len.stream().max(Integer::compareTo).get();
System.out.println(IntStream.range(0, len.size()).filter(ix -> len.get(ix).intValue() == max).boxed()
            .collect(Collectors.toList()));

answered Feb 24, 2017 at 8:39

Andrei G

6705 gold badges12 silver badges20 bronze badges

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

6 Comments

Andrei G Over a year ago

Of course you have to handle the case when max is not present

Eugene Over a year ago

but that would stream twice... interesting if it can be done with a single stream.

Andreas Over a year ago

.intValue() is unnecessary. Java will auto-unbox.

Andreas Over a year ago

Changing first line to int max = len.stream().mapToInt(Integer::intValue).max().orElse(0); would resolve issue raised by @grozandrei.

Karthik Bharadwaj Over a year ago

can use int max = Collections.max(len); function to get Max value

|

Flown · Accepted Answer · 2017-02-24 12:25:00Z

3

It is possible to use only one Stream pipeline:

List<Integer> len = Arrays.asList(9, 3, 6, 5, 4, 9);

List<Integer> indices = IntStream.range(0, len.size()).boxed()
    .collect(Collectors.collectingAndThen(
        Collectors.groupingBy(len::get, TreeMap::new, Collectors.toList()),
        m -> m.isEmpty() ? Collections.emptyList() : m.lastEntry().getValue()));
System.out.println(indices);

First group your indices to the respective values in your list. Then you have to decide what to do if the intermediate map is empty. Either you throw an NoSuchElementException or return an empty list. In my example I chose the latter case.

Result:

[0, 5]

answered Feb 24, 2017 at 12:25

Flown

11.8k3 gold badges50 silver badges63 bronze badges

1 Comment

Eugene Over a year ago

pretty nice :) one plus

Markus Benko · Accepted Answer · 2017-02-24 08:54:12Z

1

If the result doesn't have to be a Stream or Optional you could accomplish the task using this code:

IntStream.range(0, len.size()).boxed()
    .sorted(Comparator.comparing((Integer i) -> len.get(i)).reversed())
    .reduce(-1, (ixMax, ix) -> {
        if (ixMax == -1 || len.get(ixMax) == len.get(ix)) {
            System.out.println("Index -" + ix);
            return ix;
        } else {
            return ixMax;
        }
    });

Although answering the question it's probably neither concise nor very performant to be honest. With some work it should be possible to replace the if-else block with code making use of Optional.

answered Feb 24, 2017 at 8:54

Markus Benko

1,5179 silver badges8 bronze badges

Collectives™ on Stack Overflow

How to get index of multiple maximum value in List

3 Answers 3

6 Comments

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

6 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related