Java8 - Streams - Convert multidiamentional array to list

[Atul More]

Hi,

Can anybody tell me, how I can convert multidiamentional to list?
E.g. - I have an array like this:

int [][] sizeData = new int[][] {{2, 3, 4}, {5, 6}, {7, 8}};

I want to convert it into list.


Atul

[Atul More]

Hi,

There are ways to do that, I found one of them:

		int [] reqData = new int[] {2, 3, 4, 7, 1};
		List<Integer> reqDataList = Arrays.stream(reqData).boxed().collect(Collectors.toList());

                int [][] sizeData = new int[][] {{2, 3, 4}, {5, 6}, {7, 8}};
		List<List<Integer>> sizeDataList = Arrays.stream(sizeData).map(x -> Arrays.stream(x).boxed().collect(Collectors.toList())).collect(Collectors.toList());

[Jeanne Boyarsky]

Have a cow for answering your own question so quickly!

[Atul More]

Hi Jeanne,

No, I was in between the steps when I asked the question and was able to solved immediately after.
So update the answer. Nothing else.

[Campbell Ritchie]

Your post has proven useful to somebody else
You said you wanted to convert the array to a List, but there are two possible interpretations of that statement. One would create a List<int[]> and the other a List<List<Integer>>. You obviously wanted the second type of List.

[Ramón García]

Another solution may be a customized collector like this:

List a = Arrays.stream(sizeData).collect(
				ArrayList::new,                                                             //supplier 
				(x,y)-> x.addAll(IntStream.of(y).boxed().collect(Collectors.toList())),     //accumulator 
				(x,y)-> x.addAll(y));                                                       //combiner

[Paweł Baczyński]

Another solution using flatMap.

List<Integer> list = Arrays.stream(array).flatMap(arr -> Arrays.stream(arr).boxed()).collect(Collectors.toList());

...or if you think Stream.of reads better:

List<Integer> list = Stream.of(array).flatMap(arr -> IntStream.of(arr).boxed()).collect(Collectors.toList());

[Stephan van Hulst]

My personal favorite would be a small tweak to Paweł's first version:

import static java.util.Arrays.stream;
import static java.util.stream.Collectors.toList;

...

stream(array).flatMapToInt(Arrays::stream).boxed().collect(toList());