Node: Matrices in Objects

[gensjaak]

Hello team,

I'm a little confused about this. What am I doing wrong ?

Grids = {}

// I have to init matrix, fill cells with 0
Grids['grid_1'] = new Array(5).fill(new Array(5).fill(0))

// And here, just update a cell's value
// The cell x = 1, y = 3 in the grid ['grid_1'] should take => 1
Grids['grid_1'][1][3] = 1

// But, it doesn't works this way
console.log(Grids)

// I have this instead
grid_1: Array(5)
        0: (5) [0, 0, 0, 1, 0]
        1: (5) [0, 0, 0, 1, 0]
        2: (5) [0, 0, 0, 1, 0]
        3: (5) [0, 0, 0, 1, 0]
        4: (5) [0, 0, 0, 1, 0]

Thanks

[flexbox]

I think you can drop .fill

Grids['grid_1'] = Array.apply(null, {length: 5}).map(() => Array(5).fill(0))

@phareal feel free to close the issue if your problem is solved 😉

[immortal-tofu]

It's totally normal. You fill your first array with the same array.
new Array(5).fill(0) will return one new array, and you put this array in [0], [1], [2], ... So if you change it with Grids['grid_1'][1][3] = 1, you change this unique array, so you have the modification in all keys of grid_1.

Like said before, you have to create a new Array for each index (with a .map for example)

[vsemozhetbyt]

You can also use Array.from() with array-like object and map function argument:

Grids['grid_1'] = Array.from({length: 5}, row => new Array(5).fill(0));

[vsemozhetbyt]

Or, because Array.from() does not ignore holes, this also suffices:

Grids['grid_1'] = Array.from(new Array(5), row => new Array(5).fill(0));

[gensjaak]

Nice thanks.