js group objects in array

1function groupArrayOfObjects(list, key) {
2  return list.reduce(function(rv, x) {
3    (rv[x[key]] = rv[x[key]] || []).push(x);
4    return rv;
5  }, {});
6};
7
8var people = [
9    {sex:"Male", name:"Jeff"},
10    {sex:"Female", name:"Megan"},
11    {sex:"Male", name:"Taylor"},
12    {sex:"Female", name:"Madison"}
13];
14var groupedPeople=groupArrayOfObjects(people,"sex");
15console.log(groupedPeople.Male);//will be the Males 
16console.log(groupedPeople.Female);//will be the Females

1function groupByKey(array, key) {
2   return array
3     .reduce((hash, obj) => {
4       if(obj[key] === undefined) return hash; 
5       return Object.assign(hash, { [obj[key]]:( hash[obj[key]] || [] ).concat(obj)})
6     }, {})
7}
8
9
10var cars = [{'make':'audi','model':'r8','year':'2012'},{'make':'audi','model':'rs5','year':'2013'},{'make':'ford','model':'mustang','year':'2012'},{'make':'ford','model':'fusion','year':'2015'},{'make':'kia','model':'optima','year':'2012'}];
11
12var result = groupByKey(cars, 'make');
13
14JSON.stringify(result,"","\t");
15{
16	"audi": [
17		{
18			"make": "audi",
19			"model": "r8",
20			"year": "2012"
21		},
22		{
23			"make": "audi",
24			"model": "rs5",
25			"year": "2013"
26		}
27	],
28	"ford": [
29		{
30			"make": "ford",
31			"model": "mustang",
32			"year": "2012"
33		},
34		{
35			"make": "ford",
36			"model": "fusion",
37			"year": "2015"
38		}
39	],
40	"kia": [
41		{
42			"make": "kia",
43			"model": "optima",
44			"year": "2012"
45		}
46	]
47}

1result = array.reduce((h, obj) => Object.assign(h, { [obj.key]:( h[obj.key] || [] ).concat(obj) }), {})

1let group = cars.reduce((r, a) => { console.log("a", a); console.log('r', r); r[a.make] = [...r[a.make] || [], a]; return r;}, {});console.log("group", group);