Remove null from old 2d array and put the not null elements in a new 2d array

问题

I am trying to remove the null elements from the old 2d array and put it in a new 2d array, but the new 2d array is outputting all null elements.

String[][] status = new String[P][M];
String[][] newStatus = new String[P][M];

for (int i = 0; i < status.length; i++) {
    for (int j = 0; j < status.length; j++) {
        if (status[i][j] != null) {
            newStatus[i][j] = status[i][j];
        }
    }
}

Original 2d array:

[[O, X, null, O, O, null, null], [null, null, O, null, null, O, O]]

I want it to look like this:

[[O, X, O, O], [O, O, O]]

It's outputting this:

[[null, null, null, null, null, null, null],
 [null, null, null, null, null, null, null]]

I am not that familiar with 2d arrays, so if someone could help it would be much appreciated. Thank you

回答1:

You can iterate over this array and for each row filter out the null elements and collect the remaining ones toArray:

String[][] arr1 = {
        {"O", "X", null, "O", "O", null, null},
        {null, null, "O", null, null, "O", "O"}};

String[][] arr2 = Arrays.stream(arr1)
        .map(row -> Arrays.stream(row)
                // filter out null elements
                .filter(Objects::nonNull)
                // new array
                .toArray(String[]::new))
        .toArray(String[][]::new);

// output
Arrays.stream(arr2).map(Arrays::toString).forEach(System.out::println);

[O, X, O, O]
[O, O, O]

^{See also: Move null elements for each row in 2d array to the end of that row}

回答2:

I'd try this to get the values correctly replaced, assuming status has had values assigned. The problem is that arrays are a fixed size (in this case P by M), so unless you're replacing the null values with something, you can't decrease the size of the 2D array, or have each row/column vary in length from the previous, imagine 2D arrays as a fixed grid of squares and each value is on a corner.

String[][] status = new String[P][M];
String[][] newStatus = new String[P][M];

for (int i = 0; i < status.length; i++) {
    int y = 0;
    for (int j = 0; j < status.length; j++) {
        if (status[i][j] != null) {
            newStatus[i][j - y] = status[i][j];
        } else {
            newStatus[i][M - y - 1] = " ";
            y++;
        }
    }
}

this should provide

[[O,X,O,O, , , ],[O, O, O, , , , ]]

来源：https://stackoverflow.com/questions/64202403/remove-null-from-old-2d-array-and-put-the-not-null-elements-in-a-new-2d-array

标签

java

arrays

sorting

multidimensional-array

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