$arrayToObject

The $arrayToObject operator transforms an array of key-value documents into a single document (object).

---

📌 Syntax

{ "$arrayToObject": <arrayExpression> }

Each array element must be a document with "k" (key) and "v" (value) fields.

---

✅ Base Example – Convert Array to Object

📥 Input Document

{
  "pairs": [
    { "k": "a", "v": 1 },
    { "k": "b", "v": 2 }
  ]
}

📌 Expression

{ "$arrayToObject": "$pairs" }

📤 Output

{ "a": 1, "b": 2 }

---

🧱 Ecommerce Example – Reconstruct Dynamic Attributes

📌 Pipeline

[
  {
    "$project": {
      "product": "$name",
      "properties": {
        "$arrayToObject": "$attributes"
      }
    }
  }
]

📥 Input Document

{
  "name": "Shoes",
  "attributes": [
    { "k": "color", "v": "Black" },
    { "k": "size", "v": "42" }
  ]
}

📤 Output

{
  "product": "Shoes",
  "properties": {
    "color": "Black",
    "size": "42"
  }
}

---

🔧 Common Use Cases

• Reconstruct flattened key-value arrays
• Transform map-reduce style output
• Enable object-style access to filtered key-value results

---

🔗 Related Operators

• $objectToArray, $map, $mergeObjects, $getField, $setField

---

🧠 Notes

• Input array must be in [{k, v}] format
• Duplicate keys will overwrite earlier values

---