Group by data types

tl;dr.

JavaScript's array may contain different types of data. From the given array, I want to be able to group them by their types. Write a function that takes in an array, extract each data and group them by their types, and returns a new array consisting of these groups or sub-arrays.

//

I came across an interesting problem today. Given an array with various values, the task is to extract the data based on their types, regroup them, and return those groups in an array. You can assume that the given array will never be empty. So here's an example. Let say the input is [1, true, 2, false], the expected output should be [[1, 2], [true, false]].

Here's another example. If the input is [[1, 2], 1, null, true], the output should be [[[1,2]], [1], [null], [true]]. In this case, there are four types present in the array: objects, numbers, null values, and booleans.

function sortTypes(arr) {  
  let answer = []
  return answer
}

Below is my solution to the problem.

function sortTypes(arr) {
	let answer = []
	let map = new Map()

	arr.forEach(data => {
		if(data === null) {
			if(map.has('null')) {
				map.get('null').push(data)
			} else {
				map.set('null', null)
			}
		}
		else if(map.has(typeof data)) {
			map.get(typeof data).push(data)
		} else {
			map.set(typeof data, [data])
		}
	})

	for(let [key, value] of map) {
		answer.push(value)
	}

	return answer
}

let x = sortTypes([1, true, 2, false])
let y = sortTypes([[1,2],1,null,true, undefined])
console.log(x)
console.log(y)

The operations used with map (map.get, map.has, map.set) are generally O(1). I used two loops using forEach and for..of which is linear.

The overall time complexity of this algorithm is O(N).

[interview question; I don't remember from which company]