$rand (misc. query)

APPLIES TO: MongoDB vCore

The $rand operator generates a random float value between 0 and 1. This is useful for random sampling of documents or creating random values in aggregation pipelines.

Syntax

The syntax for the $rand operator is as follows:

{ $rand: {} }

Example

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

db.stores.aggregate([
   { 
     $project: {
       name: 1,
       randomValue: { $rand: {} },
       "sales.totalSales": 1
     }
   },
   { $limit: 2 }
])

This query adds a random value to each store document. When executed, it might return something like:

[
  {
    "_id": "2cf3f885-9962-4b67-a172-aa9039e9ae2f",
    "name": "First Up Consultants | Bed and Bath Center - South Amir",
    "randomValue": 0.7645893472947384,
    "sales": {
      "totalSales": 37701
    }
  },
  {
    "_id": "40d6f4d7-50cd-4929-9a07-0a7a133c2e74",
    "name": "Proseware, Inc. | Home Entertainment Hub - East Linwoodbury",
    "randomValue": 0.23456789012345678,
    "sales": {
      "totalSales": 151864
    }
  }
]

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