Suppose, we have a 2-D array like this −
const arr = [ [3, 1], [2, 12], [3, 3] ];
We are required to write a JavaScript function that takes in one such array.
The function should then create a new 2-D array that contains all elements initialized to undefined other than the element's index present in the input array.
Therefore, for the input array,
output[3][1] = 1; output[2][12] = 1; output[3][3] = 1;
And rest all elements should be initialized to undefined
Therefore, the final output should look like −
const output = [ undefined, undefined, [ undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, 1 ], [ undefined, 1, undefined, 1 ] ];
Example
The code for this will be −
const arr = [
[3, 1],
[2, 12],
[3, 3]
];
const map2D = (arr = []) => {
const res = [];
arr.forEach(el => {
res[el[0]] = res[el[0]] || [];
res[el[0]][el[1]] = 1;
});
return res;
};
console.log(map2D(arr));Output
And the output in the console will be −
[ <2 empty items>, [ <12 empty items>, 1 ], [ <1 empty item>, 1, <1 empty item>, 1 ] ]