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$maxN

The `$maxN` operator is used to retrieve the top N values for a field based on a specified filtering criteria. It's useful for identifying the highest values in a dataset.

Syntax

{
  $maxN: {
    input: <field or expression>,
    n: <number of values to retrieve>
  }
}

Parameters

inputobjectrequired

Specifies the field or expression to evaluate for maximum values.

nnumberrequired

Specifies the number of maximum values to retrieve. Must be a positive integer.

Examples

Sample Data

{
  "_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
  "name": "Lakeshore Retail | DJ Equipment Stop",
  "sales": {
    "salesByCategory": [
      { "categoryName": "DJ Headphones", "totalSales": 35921 }
    ],
    "fullSales": 3700
  }
}

Retrieve top two sales categories

Retrieve the top two sales categories with the highest sales volume per store.

This query uses $maxN as an accumulator to find the top two sales categories.

Query:

db.stores.aggregate([
  {
    $project: {
      topSalesCategories: {
        $maxN: {
          input: "$sales.salesByCategory",
          n: 2
        }
      }
    }
  },
  { $limit: 4 }
])

Output:

[
  {
    "_id": "a715ab0f-4c6e-4e9d-a812-f2fab11ce0b6",
    "topSalesCategories": [
      { "categoryName": "Stockings", "totalSales": 25731 }
    ]
  },
  {
    "_id": "94792a4c-4b03-466b-91f6-821c4a8b2aa4",
    "topSalesCategories": [
      { "categoryName": "Travel Backpacks", "totalSales": 13189 },
      { "categoryName": "Suitcases", "totalSales": 37858 }
    ]
  }
]

Using $maxN as array-expression

Retrieve the top three sales values from all sales categories for a specific store.

This query uses $maxN as an array expression to find the top three sales values.

Query:

db.stores.aggregate([
  { $match: {"_id": "40d6f4d7-50cd-4929-9a07-0a7a133c2e74"} },
  {
    $project: {
      name: 1,
      topThreeSales: {
        $maxN: {
          input: "$sales.salesByCategory.totalSales",
          n: 3
        }
      }
    }
  }
])

Output:

[
  {
    "_id": "40d6f4d7-50cd-4929-9a07-0a7a133c2e74",
    "name": "Proseware, Inc. | Home Entertainment Hub",
    "topThreeSales": [43522, 32272, 28946]
  }
]

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