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# \$1setIntersection
<a name="setIntersection"></a>

Amazon DocumentDB 中的`$setIntersection`運算子用於傳回兩個或多個陣列之間的常見元素。此運算子在使用資料集時特別有用，可讓您尋找多個集合的交集。

**參數**
+ `array1`：要交集的第一個陣列。
+ `array2`：要交集的第二個陣列。
+ `arrayN`：（選用） 要交集的其他陣列。

## 範例 (MongoDB Shell)
<a name="setIntersection-examples"></a>

下列範例示範如何使用 `$setIntersection`運算子來尋找兩個陣列之間的常見元素。

**建立範例文件**

```
db.collection.insertMany([
  { _id: 1, colors: ["red", "blue", "green"] },
  { _id: 2, colors: ["blue", "yellow", "orange"] },
  { _id: 3, colors: ["red", "green", "purple"] }
])
```

**查詢範例**

```
db.collection.aggregate([
  { $project: {
      _id: 1,
      commonColors: { $setIntersection: ["$colors", ["red", "blue", "green"]] }
    }
  }
])
```

**輸出**

```
[
  { "_id": 1, "commonColors": ["red", "blue", "green"] },
  { "_id": 2, "commonColors": ["blue"] },
  { "_id": 3, "commonColors": ["red", "green"] }
]
```

## 程式碼範例
<a name="setIntersection-code"></a>

若要檢視使用 `$setIntersection`命令的程式碼範例，請選擇您要使用的語言標籤：

------
#### [ Node.js ]

```
const { MongoClient } = require('mongodb');

async function example() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');
  const collection = db.collection('mycollection');

  const result = await collection.aggregate([
    {
      $project: {
        _id: 1,
        commonColors: { $setIntersection: ["$colors", ["red", "blue", "green"]] }
      }
    }
  ]).toArray();

  console.log(result);
  client.close();
}

example();
```

------
#### [ Python ]

```
from pymongo import MongoClient

def example():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client['test']
    collection = db['mycollection']

    result = list(collection.aggregate([
        {
            '$project': {
                '_id': 1,
                'commonColors': { '$setIntersection': ["$colors", ["red", "blue", "green"]] }
            }
        }
    ]))

    print(result)
    client.close()

example()
```

------