fastify-riotjs-and-lowdb/node_modules/collect.js/docs/api/flatten.md

flatten()

The flatten method flattens a multi-dimensional collection into a single dimension:

const collection = collect({
  club: 'Liverpool',
  players: ['Salah', 'Firmino', 'Mané'],
});

const flattened = collection.flatten();

flattened.all();

// ['Liverpool', 'Salah', 'Firmino', 'Mané'];

You may optionally pass the function a "depth" argument:

const collection = collect({
  Apple: [
    {
      name: 'iPhone 6S',
      brand: 'Apple',
    },
  ],
  Samsung: [
    {
      name: 'Galaxy S7',
      brand: 'Samsung',
    },
  ],
});

const flattened = collection.flatten(1);

flattened.all();

// [
//   { name: 'iPhone 6S', brand: 'Apple' },
//   { name: 'Galaxy S7', brand: 'Samsung' },
// ]

In this example, calling flatten without providing the depth would have also flattened the nested arrays, resulting in ['iPhone 6S', 'Apple', 'Galaxy S7', 'Samsung']. Providing a depth allows you to restrict the levels of nested arrays that will be flattened.

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