Syntax
{
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$facet: {
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facetName1: [<stage1>, <stage2>, <stage3>],
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facetName2: [<stage4>, <stage5>, …],
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...
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}
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}
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Examples
> db.example.insert([
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{
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_id: "product1",
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avgReview: 4.3,
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price: 21,
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category: "TVs",
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title: "Sony 42 inch HDTV",
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attributes: [
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{name: "type", value: "HD"},
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{name: "screen size", value: 42},
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{name: "manufacturer", value: "Sony"},
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...
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]
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}
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...
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])
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> db.example.aggregate([
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{$match: {category: "TVs"}}, // Match all relevant results.
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{$facet: {
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"Screen Sizes": [
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{$unwind: "$attributes"},
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{$match: {"attributes.name": "screen size"}},
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{$group: {
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_id: { /* Use $switch to compute buckets for screen sizes */ },
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count: {$sum: 1}
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}}
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],
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"Manufacturer": [
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{$match: {"attributes.name": "manufacturer"}},
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{$group: {_id: "$attributes.value", count: {$sum: 1}}},
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{$sort: {count: -1}}
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{$limit: 5}
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]
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}}
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])
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// Output.
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{
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"Screen Size": [
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{_id: {min: MinKey, max: 32}, count: 32},
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{_id: {min: 32, max: 42}, count: 32},
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{_id: {min: 42, max: 50}, count: 33},
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{_id: {min: 50, max: MaxKey}, count: 33}
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],
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"Manufacturer": [
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{_id: "Sony", count: 54},
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{_id: "Samsung", count: 45},
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{_id: "LG", count: 34},
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{_id: "Sharp", count: 22},
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{_id: "Vizio", count: 14},
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]
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}
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Behavior
- names of sub-pipelines (keys in the document) must be unique.
- This is a blocking stage.
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