$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

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

Example

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

{
  "_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

The following example helps you determine if all of a store's categories are included in their promotion discounts, and vice versa.

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"
        ]
      }
    }
  }
])

The 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).

{
  "_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
}

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