create new arrays for repeating elements in javasc

问题:

I have a JavaScript array with 8 elements and some elements are repeating. I want to create separate arrays for identical elements.

example: original array is [1,1,1,3,3,1,2,2] resulting arrays will be [1,1,1,1],[3,3],[2,2]

I want a function similar to this:

var array=[1,1,1,3,3,1,2,2];



var createNewArrays=function(array){
     for (var i = 0; i < array.length; i++) {
        for (var j = 0; j < array.length; j++) {

        }
    }
   
};

回答1:

You could use a hash table as reference to the sub arrays for the collection.

var array = [1, 1, 1, 3, 3, 1, 2, 2],
    result = [];

array.forEach(function (a) {
    a in this || result.push(this[a] = []);
    this[a].push(a);
}, Object.create(null));

console.log(result);

回答2:

var arr = [1,1,1,3,3,1,2,2];

var hash = Object.create(null);

var result = arr.reduce(function(r, n) {
  if(!hash[n]) {
    hash[n] = [];
    r.push(hash[n]);
  }
  
  hash[n].push(n);
  
  return r;
}, []);

console.log(result);

And an ES6 solution that uses Map, and spread:

const arr = [1,1,1,3,3,1,2,2];

const result = [...arr.reduce((r, n) =>
  r.set(n, (r.get(n) || []).concat(n)),
new Map()).values()];

console.log(result);

回答3:

Let's assume you want the resulting arrays to be properties on an object keyed by the value they represent. You just loop through the array, creating or adding to the arrays on the object properties as you go:

var array=[1,1,1,3,3,1,2,2];
var result = {};
array.forEach(function(entry) {
  (result[entry] = result[entry] || []).push(entry);
});
console.log(result);

That's a bit dense, here's a clearer version:

var array=[1,1,1,3,3,1,2,2];
var result = {};
array.forEach(function(entry) {
  var subarray = result[entry];
  if (!subarray) {
    subarray = result[entry] = [];
  }
  subarray.push(entry);
});
console.log(result);