$indexOfArray

The $indexOfArray operator returns the index of the first occurrence of a value in an array.

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📌 Syntax

{ "$indexOfArray": [ <arrayExpression>, <searchValue>, <start>, <end> ] }

• arrayExpression: The array to search
• searchValue: The value to search for
• start: (optional) Index to start searching from
• end: (optional) Index to end searching (exclusive)

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✅ Base Example – Find Index of Value

📥 Input Document

{ "tags": ["sale", "new", "hot"] }

📌 Expression

{ "$indexOfArray": ["$tags", "new"] }

📤 Output

1

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✅ Base Example – Value Not Found

📥 Input Document

{ "tags": ["sale", "hot"] }

📌 Expression

{ "$indexOfArray": ["$tags", "exclusive"] }

📤 Output

-1

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🧱 Ecommerce Example – Position of Top-Selling Product

📌 Pipeline

[
  {
    "$project": {
      "productRank": {
        "$indexOfArray": ["$topProducts", "SKU-1002"]
      }
    }
  }
]

📥 Input Document

{
  "topProducts": ["SKU-1001", "SKU-1002", "SKU-1003"]
}

📤 Output

{ "productRank": 1 }

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🔧 Common Use Cases

• Determine item positions
• Ranking systems
• Validation of list order

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🔗 Related Operators

• $arrayElemAt, $slice, $filter, $indexOfBytes, $indexOfCP

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🧠 Notes

• Returns -1 if not found.
• Use with $cond to handle missing values gracefully.

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