Rewrite the title as: Group main array and add fields and subarrays in each grouping

Question

I have a heavy array like this:

[
  {Id: 1, Name: 'Red', optionName: 'Color'},
  {Id: 2, Name: 'Yellow', optionName: 'Color'},
  {Id: 3, Name: 'Blue', optionName: 'Color'},
  {Id: 4, Name: 'Green', optionName: 'Color'},
  {Id: 7, Name: 'Black', optionName: 'Color'},
  {Id: 8, Name: 'S', optionName: 'Size'},
  {Id: 11, Name: 'M', optionName: 'Size'},
  {Id: 12, Name: 'L', optionName: 'Size'},
  {Id: 13, Name: 'XL', optionName: 'Size'},
  {Id: 14, Name: 'XXL', optionName: 'Size'}
]

I need to group by optionName and have two rows in the main array, like this:

[
  {
    Name: 'Color',
    Data:[{Id: 1, Name: 'Red'},
          {Id: 2, Name: 'Yellow'},
          {Id: 3, Name: 'Blue'},
          {Id: 4, Name: 'Green'},
          {Id: 7, Name: 'Black'}]
  }, {
    Name: 'Size',
    Data:[{Id: 8, Name: 'S'},
          {Id: 11, Name: 'M'},
          {Id: 12, Name: 'L'},
          {Id: 13, Name: 'XL'},
          {Id: 14, Name: 'XXL'}]
  }
]

How to implement it in javascript?

Answer 1

An ES6 solution using Map object:

function groupBy(arr, key) {
  	return arr.reduce(
      (sum, item) => {
      	const groupByVal = item[key];
        groupedItems = sum.get(groupByVal) || [];
        groupedItems.push(item);
      	return sum.set(groupByVal, groupedItems);
        },
      new Map()
      );
}

var Data = [ 
{ Id: 1, Name: 'Red', optionName: 'Color' }, 
  { Id: 2, Name: 'Yellow', optionName: 'Color' },
  { Id: 3, Name: 'Blue', optionName: 'Color' },
  { Id: 4, Name: 'Green', optionName: 'Color' },
  { Id: 7, Name: 'Black', optionName: 'Color' },
  { Id: 8, Name: 'S', optionName: 'Size' },
  { Id: 11, Name: 'M', optionName: 'Size' },
  { Id: 12, Name: 'L', optionName: 'Size' },
  { Id: 13, Name: 'XL', optionName: 'Size' },
  { Id: 14, Name: 'XXL', optionName: 'Size' } ];

document.getElementById("showArray").innerHTML =JSON.stringify([...groupBy(Data, 'optionName')], null, 4); 

<pre id="showArray"></pre>

Answer 2

Here is the code snippet I wrote for this situation. You can add this function to all arrays:

Object.defineProperty(Array.prototype, 'group', {
  enumerable: false,
  value: function (key) {
    var map = {};
    this.forEach(function (e) {
      var k = key(e);
      map[k] = map[k] || [];
      map[k].push(e);
    });
    return Object.keys(map).map(function (k) {
      return {key: k, data: map[k]};
    });
  }
});

You can use it like this. You just pass a function that defines how to group the data.

var newArray = arr.group(function (item) {
  return item.optionName;
});

Working Fiddle

If necessary, you can replace {key: k, data: map[k]} with {Name: k, Data: map[k]}.

---

This is also a more compact ES6 version of the above code:

Object.defineProperty(Array.prototype, 'group', {
  enumerable: false,
  value: function (key) {
    let map = {};
    this.map(e => ({k: key(e), d: e})).forEach(e => {
      map[e.k] = map[e.k] || [];
      map[e.k].push(e.d);
    });
    return Object.keys(map).map(k => ({key: k, data: map[k]}));
  }
});

Use it like this:

let newArray = arr.group(item => item.optionName))