$min

The $min operator returns the smallest value from a list of expressions or grouped values.

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📌 Syntax

{ "$min": <expression> }

Used in: - $group (accumulator) - Array contexts (e.g., $map, $reduce) - Arithmetic expressions

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✅ Base Example – Minimum in Array

📥 Input Document

{ "numbers": [15, 5, 8] }

📌 Expression

{ "$min": "$numbers" }

📤 Output

5

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🧱 Ecommerce Example – Minimum Discounted Price Per Brand

📌 Pipeline

[
  { "$unwind": "$items" },
  {
    "$group": {
      "_id": "$items.brand",
      "minPrice": { "$min": "$items.price" }
    }
  }
]

📥 Input Documents

[
  {
    "items": [
      { "brand": "A", "price": 50 },
      { "brand": "A", "price": 30 },
      { "brand": "B", "price": 40 }
    ]
  }
]

📤 Output

[
  { "_id": "A", "minPrice": 30 },
  { "_id": "B", "minPrice": 40 }
]

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🔧 Common Use Cases

• Calculate lowest value in a group
• Use in price comparisons
• Extract min date/time in event logs

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🔗 Related Operators

• $max, $avg, $first, $last, $reduce

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🧠 Notes

• In $group, must be used with grouped documents
• Use with caution on mixed-type arrays

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