$maxN (array expression)

APPLIES TO: MongoDB vCore

The $maxN operator returns the n largest values from an array. It's useful when you want to find the top performing items based on numerical values, such as the highest sales figures or largest discount percentages.

Syntax

The syntax for the $maxN operator is as follows:

{
  $maxN: {
    input: <array>,
    n: <number>
  }
}

Parameters

Description
input The array from which to return the n largest values. The array should contain numerical values.
n The number of largest values to return. Must be a positive integer.

Example

Let's understand the usage with sample json from stores dataset.

{
  "_id": "40d6f4d7-50cd-4929-9a07-0a7a133c2e74",
  "name": "Proseware, Inc. | Home Entertainment Hub - East Linwoodbury",
  "sales": {
    "totalSales": 151864,
    "salesByCategory": [
      {
        "categoryName": "Sound Bars",
        "totalSales": 2120
      },
      {
        "categoryName": "Home Theater Projectors",
        "totalSales": 45004
      },
      {
        "categoryName": "Game Controllers",
        "totalSales": 43522
      },
      {
        "categoryName": "Remote Controls",
        "totalSales": 28946
      },
      {
        "categoryName": "VR Games",
        "totalSales": 32272
      }
    ]
  },
  "promotionEvents": [
    {
      "eventName": "Major Bargain Bash",
      "discounts": [
        {
          "categoryName": "Sound Bars",
          "discountPercentage": 9
        },
        {
          "categoryName": "VR Games",
          "discountPercentage": 7
        },
        {
          "categoryName": "Xbox Games",
          "discountPercentage": 25
        },
        {
          "categoryName": "Projector Accessories",
          "discountPercentage": 18
        },
        {
          "categoryName": "Mobile Games",
          "discountPercentage": 8
        },
        {
          "categoryName": "Projector Cases",
          "discountPercentage": 22
        }
      ]
    }
  ]
}

Example 1: Get top three sales values

Suppose you want to find the top three sales values from all sales categories.

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

This produces the following output:

[
  {
    _id: '40d6f4d7-50cd-4929-9a07-0a7a133c2e74',
    name: 'Proseware, Inc. | Home Entertainment Hub - East Linwoodbury',
    topThreeSales: [ 45004, 43522, 32272 ]
  }
]

Example 2: Get highest discount percentages

You can also use $maxN to find the highest discount percentages from a promotion event.

db.stores.aggregate([
  { $match: {"_id": "40d6f4d7-50cd-4929-9a07-0a7a133c2e74"} },
  { $unwind: "$promotionEvents" },
  { $match: {"promotionEvents.eventName": "Major Bargain Bash"} },
  {
    $project: {
      name: 1,
      eventName: "$promotionEvents.eventName",
      topTwoDiscounts: {
        $maxN: {
          input: "$promotionEvents.discounts.discountPercentage",
          n: 2
        }
      }
    }
  }
])

This produces the following output:

[
  {
    _id: '40d6f4d7-50cd-4929-9a07-0a7a133c2e74',
    name: 'Proseware, Inc. | Home Entertainment Hub - East Linwoodbury',
    eventName: 'Major Bargain Bash',
    topTwoDiscounts: [ 25, 22 ]
  }
]

Example 3: Compare top sales across multiple stores

You can use $maxN to compare the top sales values across different stores.

db.stores.aggregate([
  {
    $project: {
      name: 1,
      topTwoSales: {
        $maxN: {
          input: "$sales.salesByCategory.totalSales",
          n: 2
        }
      }
    }
  },
  { $limit: 3 }
])

This query returns the top two sales values for the first three stores in the collection, making it easy to compare performance across different locations.

[
  {
    _id: 'af9015d8-3f6b-455f-8967-a83cc22ff018',
    name: 'VanArsdel, Ltd. | Party Goods Nook - Kunzeshire',
    topTwoSales: [ 3526 ]
  },
  {
    _id: 'ed319c06-731d-45fc-8a47-b05af8637cdf',
    name: 'Relecloud | Computer Outlet - Langoshfort',
    topTwoSales: [ 46356, 41111 ]
  },
  {
    _id: '62438f5f-0c56-4a21-8c6c-6bfa479494ad',
    name: 'First Up Consultants | Plumbing Supply Shoppe - New Ubaldofort',
    topTwoSales: [ 36202, 32306 ]
  }
]

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