如何遍历映射并将具有相似值的键推送到同一个数组中？

Question

I've got javascript map with structure like this:

let map = {3 => 1,
           15 => 2,
           0 => 2,
           8 => 3,
           9 => 3}

I need to receive the arrays of keys, and keys with similar values should be in the same array.

[[3], [15,0],[8,9]]

This is what I've tried:

    let answers = [];
    let currentVal = 1;
    map.forEach((value, key)=>{
      let subArr = [];
      if(value === currentVal){
        subArr.push(key);
        answers.push(subArr);
        currentVal++;
   }

    });
    
    return answers;

And it returns [[3], [15], [8]]

Answer 1

I assume your map is an object, not map for readability reasons, but if u are using Map there you can change methods to get elements but main idea you can see below:

 const data = { 3: 1, 15: 2, 0: 2, 8: 3, 9: 3 }; const customData = Object.entries(data).reduce((acc, [key, value]) => { if (value in acc) { acc[value].push(key); } else { acc[value] = [key]; } return acc; }, {}); const finalArray = Object.values(customData); console.log(finalArray);

Edit with Map() example:

const data = new Map([
  [3, 1],
  [15, 2],
  [0, 2],
  [8, 3],
  [9, 3]
]);

const customData = Array.from(data).reduce((acc, [key, value]) => {
  if (value in acc) {
    acc[value].push(key);
  } else {
    acc[value] = [key];
  }

  return acc;
}, {});

const finalArray = Object.values(customData);
console.log(finalArray);

Answer 2

You could use Object.entries and destructuring key, value but I change their place as value, key to match the data structure map provided by OP :

 let map = { 3: 1, 15: 2, 0: 2, 8: 3, 9: 3 }; const arr = []; for (const [value, key] of Object.entries(map)) { if (arr[key]) { arr[key].push(value); } else { arr[key] = [value]; } } console.log(arr.filter(Boolean)); // [[3], [15,0],[8,9]]

NOTE arr.filter(Boolean) to remove falsy (empty) values from array since index 0 have no array inside of it!

Answer 3

Your map is not a valid one. Hence, I am creating it by using Map instance. You can have a look in this official documentation of Map Object .

Live Demo :

 // Creating a map object by using Map instance const map = new Map(); // Setting the key, values in map object. map.set(3, 1) map.set(15, 2) map.set(0, 2) map.set(8, 3) map.set(9, 3) // Declaring an empty array which will store the result. const arr = []; // Iterate over a map object and assign the keys of map object into an 'arr'. for (const [key, value] of map) { (arr[value]) ? arr[value].push(key) : arr[value] = [key]; } // Output console.log(arr.filter(Boolean));