Create an empty two dimensional array in Javascript, with keys

Question

I'm trying to create a matrix in Javascript, but one which has predefined keys for the X and Y axis.

For example I have the following keys

const x = [2,4,6,8]
const y = [10,20,40,60,80]

I found the following snippet which creates an empty two dimensional array with 4 rows and 5 columns

[...Array(4)].map(x=>Array(5).fill(0))       

I'm wondering if it's possible to create these arrays (objects), but using provided keys to go with it.

So the end result would look like this.

{
    2 => {10 => 0, 20 => 0, 40 => 0, 60 => 0, 80 => 0}
    4 => {10 => 0, 20 => 0, 40 => 0, 60 => 0, 80 => 0}
    6 => {10 => 0, 20 => 0, 40 => 0, 60 => 0, 80 => 0}
    8 => {10 => 0, 20 => 0, 40 => 0, 60 => 0, 80 => 0}
}

Answer 1

You could create the wanted objects by looping and reducing the data.

The callback of Array#reduce takes as first parameter the accumulator, here it is an object, and as second parameter the value of the iterating array.

As startValue for the reduce, it take an (kind of empty) object and usdes this object to add properties. To have this object (aka accumulator) ready for the next loop (and final result), it has to be returned.

var x = [2, 4, 6, 8],
    y = [10, 20, 40, 60, 80],
    result = x.reduce((r, k) => {
        r[k] = y.reduce((q, l) => {
            q[l] = 0;
            return q;
        }, {});
        return r;
    }, {});

console.log(result);