I have the following array:
let numbers = [10, 20, 20, 10, 10, 30, 50, 10, 20];
I create a new array without the duplicate values:
let counter = [...new Set(array)];
//Output: [ 10, 20, 30, 50 ]
I want to instantiate the counter array as a 2D/nested array so that it looks like this:
//counter output: [[10,4][20, 3][30, 1][50,1]]
What's the best way to do this? The numbers array could have various elements and therefore the number of elements in the counter array could vary.
This answer is for the original question (how to create an array of [[10, 0],[20, 0],[30, 0],[50, 0]] from the Set):
Instead of spreading the Set, use Array.from() to create an array of pairs:
const numbers = [10, 20, 20, 10, 10, 30, 50, 10, 20];
const counter = Array.from(new Set(numbers), v => [v, 0]);
console.log(counter);Assuming you actually want that second sub-array index to represent the number of occurrences of each number (ed: confirmed now), you can collect the counts into a Map and then convert that to an array
let numbers = [10, 20, 20, 10, 10, 30, 50, 10, 20];
const counter = [...numbers.reduce((map, n) =>
map.set(n, (map.get(n) ?? 0) + 1), new Map())]
console.info(JSON.stringify(counter)) // stringifying so it's all on one lineThe array conversion works since Map supports the common entries format of
[ [ key, value ], [ key, value ], ... ]
and using spread syntax implicitly converts it to an entries array.
One way is take the ideas you have already used and map across those values returning new arrays with the value and an additional zero.
let numbers = [...new Set([10, 20, 20, 10, 10, 30, 50, 10, 20])].map(value=>[value,0]);
You can convert your original array into an object (hash map) to keep track of the count. And then convert it into to Object.entries() array.
const numbers = [10, 20, 20, 10, 10, 30, 50, 10, 20];
let obj = {};
numbers.forEach(n => {
obj[n] = obj[n] || 0;
obj[n]++;
});
const counter = Object.entries(obj).map(e => [+e[0], e[1]]);
console.log(counter);
0?counter.map(c => [ c, 0 ])?