javascript reduce array of objects group by property

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

1var 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' }],
2    result = cars.reduce(function (r, a) {
3        r[a.make] = r[a.make] || [];
4        r[a.make].push(a);
5        return r;
6    }, Object.create(null));
7
8console.log(result);

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);

1var cars = [
2    {
3        'make': 'audi',
4        'model': 'r8',
5        'year': '2012'
6    }, {
7        'make': 'audi',
8        'model': 'rs5',
9        'year': '2013'
10    }, {
11        'make': 'ford',
12        'model': 'mustang',
13        'year': '2012'
14    }, {
15        'make': 'ford',
16        'model': 'fusion',
17        'year': '2015'
18    }, {'make': 'kia', 'model': 'optima', 'year': '2012'},
19];
20
21result = cars.reduce((h, car) => Object.assign(h, { [car.make]:( h[car.make] || [] ).concat({model: car.model, year: car.year}) }), {})
22
23console.log(JSON.stringify(result));