{

  $facet: {

    facetName1: [<stage1>, <stage2>, <stage3>],

    facetName2: [<stage4>, <stage5>, …],

    ...

  }

}

> db.example.insert([

    {

      _id: "product1",

      avgReview: 4.3,

      price: 21,

      category: "TVs",

      title: "Sony 42 inch HDTV",

      attributes: [

        {name: "type", value: "HD"},

        {name: "screen size", value: 42},

        {name: "manufacturer", value: "Sony"},

        ...

      ]

    }

    ...

])

> db.example.aggregate([

{$match: {category: "TVs"}},  // Match all relevant results.

{$facet: {

  "Screen Sizes": [

     {$unwind: "$attributes"},

     {$match: {"attributes.name": "screen size"}},

     {$group: {

         _id: { /* Use $switch to compute buckets for screen sizes */ },

         count: {$sum: 1}

     }}

   ],

   "Manufacturer": [

     {$match: {"attributes.name": "manufacturer"}},

     {$group: {_id: "$attributes.value", count: {$sum: 1}}},

     {$sort: {count: -1}}

     {$limit: 5}

   ]

}}

])

// Output.

{

  "Screen Size": [

    {_id: {min: MinKey, max: 32}, count: 32},

    {_id: {min: 32, max: 42}, count: 32},

    {_id: {min: 42, max: 50}, count: 33},

    {_id: {min: 50, max: MaxKey}, count: 33}

  ],

  "Manufacturer": [

    {_id: "Sony", count: 54},

    {_id: "Samsung", count: 45},

    {_id: "LG", count: 34},

    {_id: "Sharp", count: 22},

    {_id: "Vizio", count: 14},

  ]

}