Reducing/Grouping an array in Javascript

Question

Based on this example, I want to group by object in a slightly other way. The outcome should be as follows:

[{
  key: \"audi\"
  items: [
    {
      \"make\": \         


        

Answer 1

You could use a hash table for grouping by make and an array for the wanted result.

For every group in hash, a new object, like

{
    key: a.make,
    items: []
}

is created and pushed to the result set.

The hash table is initialized with a really empty object. There are no prototypes, to prevent collision.

var 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' }],
    hash = Object.create(null),
    result = [];

cars.forEach(function (a) {
    if (!hash[a.make]) {
        hash[a.make] = { key: a.make, items: [] };
        result.push(hash[a.make]);
    }
    hash[a.make].items.push(a);
});

console.log(result);

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