Converting IntStream into 2-dimensional array

Question

After I have flattened int [][] into IntStream. I need to "split it back" into small 2 dimensional arrays following this algorithm:

IntSream [1,2,3,4] -> int [][] finalArr {{1,2},{2,3},{3,4}}

Basically,combining two nearest elements into array. I feel that it's possible to get over using flatMap again, but I can't figure out. Any suggestions?

codeint differentSquares(int[][] matrix) { // if(matrix[0].length<2 || matrix[1].length<2)return 0; Stream<int[]> stream = Arrays.stream(matrix); IntStream intStream = stream.filter(i->i.length>=2).flatMapToInt(x->Arrays.stream(x)); // intStream.forEach(System.out::println); return ...; }code — tarmogoyf
– tarmogoyf, Commented Jan 19, 2018 at 9:28
Does the input IntStream consist of a sequence of consecutive integers (such as [1, 2, 3, 4]), or could it also be any list of numbers (such as [1, 4, 3, 2])? — fps
– fps, Commented Jan 19, 2018 at 17:06

Anurag Sharma · Accepted Answer · 2018-01-19 16:53:15Z

1

You can get List(list) from IntStream and use following code to create 2D array of two pairs:

import java.util.Arrays;
import java.util.List;
import  java.util.stream.IntStream;

public class Stream1 {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3,4);

        int [][] int2DArray = IntStream.range(1, list.size())
                .mapToObj(i -> new int[] {list.get(i-1), list.get(i)})
                .toArray(int[][]:: new);

        System.out.println(Arrays.deepToString(int2DArray));
    }
}

Prints output:

[[1, 2], [2, 3], [3, 4]]

edited Jan 19, 2018 at 16:53

answered Jan 19, 2018 at 9:40

Anurag Sharma

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9 Comments

tarmogoyf Over a year ago

The problem is that I also want to get [2 , 3] in the middle of them)

Holger Over a year ago

Since the question was specifically about an IntStream, there is no need for the List<Integer>. Further, there is no reason to use change the requested int[][] to Integer[][]. So you can do it as simple as int[][] int2DArray = IntStream.range(1, 4).mapToObj(i -> new int[] { i, i+1 }) .toArray(int[][]::new);

Anurag Sharma Over a year ago

Holger and @FedericoPeraltaSchaffner: thanks for the inputs edited to int[][]

fps Over a year ago

@AnuragSharma No, unless you use an external library, such as StreamEx. If you already have the index-based data structure (i.e. an ArrayList), the approach given in this answer is absolutely correct IMO.

Holger Over a year ago

@FedericoPeraltaSchaffner that’s giving by the OP’s example. Otherwise, we could simply use an int[] array as input. If the input is an unknown IntStream, just calling toArray() first, followed by this solution might be the simplest choice.

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