Formatting a 2d int array into a string using streams

Question

I have the following array:

private static final int[][] BOARD = {
    { 0, 0, 0, 0, 0 },
    { 0, 0, 0, 0, 0 },
    { 0, 0, 0, 0, 0 },
    { 0, 0, 0, 0, 0 },
    { 0, 0, 0, 0, 0 }
};

And I want to create a String representation on it, so if I were to print it on the console, it should look like this:

[0,0,0,0,0]
[0,0,0,0,0]
[0,0,0,0,0]
[0,0,0,0,0]
[0,0,0,0,0]

I can get this done with 2 nested for loops, but I am trying to accomplish this using streams. This is what I got so far:

public String toString() {
    StringJoiner board = new StringJoiner("\n");

    for (int i = 0; i < BOARD.length; i++) {
        board.add(
            IntStream.of(BOARD[i])
                .mapToObj(String::valueOf)
                .collect(Collectors.joining(",", "[", "]"))
        );
    }
    return board.toString();
}

Is this something possible? I'm not particularly interested in performance (feel free to add some comments on that regard if you want), I am just trying to do this in a single chain of stream operations.

`Arrays.stream(BOARD).map(Arrays::toString).map(row -> row.replace(" ", "")).collect(Collectors.joining("\n"))` — shmosel, Nov 14 '18 at 03:39

score 3 · Answer 1 · edited Nov 14 '18 at 03:40

3

You can alternatively do it using Arrays.streamas :

Arrays.stream(BOARD)
        .map(aBOARD -> IntStream.of(aBOARD)
                .mapToObj(String::valueOf)
                .collect(Collectors.joining(",", "[", "]")))
        .forEach(board::add);

edited Nov 14 '18 at 03:40

shmosel

49,289
6
73
138

answered Nov 14 '18 at 03:35

Naman

27,789
26
218
353

score 2 · Accepted Answer · answered Nov 14 '18 at 03:40

You can nest the stream and map each level together, first by commas and then by the system line separator. Like,

return Arrays.stream(BOARD).map(a -> Arrays.stream(a)
            .mapToObj(String::valueOf).collect(Collectors.joining(",", "[", "]")))
            .collect(Collectors.joining(System.lineSeparator()));

I get

[0,0,0,0,0]
[0,0,0,0,0]
[0,0,0,0,0]
[0,0,0,0,0]
[0,0,0,0,0]

Kartik · Answer 3 · 2018-11-14T03:43:05.573

Collections' toString() already provides that notation in the AbstractCollection class. Just use:-

Arrays.stream(BOARD)
        .forEach(ints -> System.out.println(
                Arrays.stream(ints).boxed().collect(Collectors.toList()))
        );

Or if you are happy to change int[][] to Integer[][], you can even do:-

Arrays.stream(BOARD)
        .forEach(ints -> System.out.println(Arrays.deepToString(ints)));

Formatting a 2d int array into a string using streams

3 Answers3