Back to DocumentationMQL Documentation

$setIsSubset

The $setIsSubset operator determines if one array is a subset of a second array.

$setIsSubset

The $setIsSubset operator returns a Boolean value that indicates if one array is a subset of a second array. It treats arrays as sets, which means it ignores duplicates and element order. It returns true if all the elements in the first array exist in the second array. Otherwise, it returns false.

Syntax

{
  $setIsSubset: [ <array1>, <array2> ]
}

Parameters

ParameterDescription
<array1>The array to check to see if it's a subset of <array2>.
<array2>The array to check against.

Examples

Consider this sample document from the stores collection.

{
  "_id": "2cf3f885-9962-4b67-a172-aa9039e9ae2f",
  "name": "First Up Consultants | Bed and Bath Center - South Amir",
  "location": {
    "lat": 60.7954,
    "lon": -142.0012
  },
  "staff": {
    "totalStaff": {
      "fullTime": 18,
      "partTime": 17
    }
  },
  "sales": {
    "totalSales": 37701,
    "salesByCategory": [
      {
        "categoryName": "Mattress Toppers",
        "totalSales": 37701
      }
    ]
  },
  "promotionEvents": [
    {
      "eventName": "Price Drop Palooza",
      "promotionalDates": {
        "startDate": {
          "Year": 2024,
          "Month": 9,
          "Day": 21
        },
        "endDate": {
          "Year": 2024,
          "Month": 9,
          "Day": 30
        }
      },
      "discounts": [
        {
          "categoryName": "Bath Accessories",
          "discountPercentage": 18
        },
        {
          "categoryName": "Pillow Top Mattresses",
          "discountPercentage": 17
        },
        {
          "categoryName": "Bathroom Scales",
          "discountPercentage": 9
        },
        {
          "categoryName": "Towels",
          "discountPercentage": 5
        },
        {
          "categoryName": "Bathrobes",
          "discountPercentage": 5
        },
        {
          "categoryName": "Mattress Toppers",
          "discountPercentage": 6
        },
        {
          "categoryName": "Hand Towels",
          "discountPercentage": 9
        },
        {
          "categoryName": "Shower Heads",
          "discountPercentage": 5
        },
        {
          "categoryName": "Bedspreads",
          "discountPercentage": 19
        },
        {
          "categoryName": "Bath Mats",
          "discountPercentage": 21
        }
      ]
    }
  ]
}

Example 1: Determine if sales categories are a subset of promotion categories

This query determines if all of a store's categories are included in their promotion discounts, and vice versa. This query returns categories included under both the sales and promotion brackets. It confirms that the sales value is a subset of a particular promotion category (but doesn't do the reverse).

db.stores.aggregate([
  { $match: {"_id": "2cf3f885-9962-4b67-a172-aa9039e9ae2f"} },
  {
    $project: {
      name: 1,
      salesCategories: "$sales.salesByCategory.categoryName",
      promotionCategories: { $arrayElemAt: ["$promotionEvents.discounts.categoryName", 0] },
      salesAreSubsetOfPromotions: {
        $setIsSubset: [
          "$sales.salesByCategory.categoryName",
          { $arrayElemAt: ["$promotionEvents.discounts.categoryName", 0] }
        ]
      },
      promotionsAreSubsetOfSales: {
        $setIsSubset: [
          { $arrayElemAt: ["$promotionEvents.discounts.categoryName", 0] },
          "$sales.salesByCategory.categoryName"
        ]
      }
    }
  }
])

This query returns the following result.

[
  {
    "_id": "2cf3f885-9962-4b67-a172-aa9039e9ae2f",
    "name": "First Up Consultants | Bed and Bath Center - South Amir",
    "salesCategories": [
      "Mattress Toppers"
    ],
    "promotionCategories": [
      "Bath Accessories",
      "Pillow Top Mattresses",
      "Bathroom Scales",
      "Towels",
      "Bathrobes",
      "Mattress Toppers",
      "Hand Towels",
      "Shower Heads",
      "Bedspreads",
      "Bath Mats"
    ],
    "salesAreSubsetOfPromotions": true,
    "promotionsAreSubsetOfSales": false
  }
]

Related content