本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

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

`$slice` 彙總運算子可讓您從陣列的開頭或結尾周遊陣列，以傳回陣列的子集。這用於顯示陣列欄位中有限數量的項目，例如頂端或底部 N 個項目。

**參數**
+ `array`：要分割的陣列欄位。
+ `n`：整數，指定要傳回的元素數目。正值從陣列的開頭開始，負值則從陣列的結尾開始。

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

下列範例示範如何使用 `$slice`傳回每個 Chef 的前兩個最愛甜食。

**建立範例文件**

```
db.sweets.insertMany([
  { "_id" : 1, "name" : "Alvin", "favorites": [ "chocolate", "cake", "toffee", "beignets" ] },
  { "_id" : 2, "name" : "Tom", "favorites": [ "donuts", "pudding", "pie" ] },
  { "_id" : 3, "name" : "Jessica", "favorites": [ "fudge", "smores", "pudding", "cupcakes" ] },
  { "_id" : 4, "name" : "Rachel", "favorites": [ "ice cream" ] }
]);
```

**查詢範例**

```
db.sweets.aggregate([
  { $project: { _id: 0, name: 1, topTwoFavorites: { $slice: [ "$favorites", 2 ] } } }
]);
```

**輸出**

```
[
  { name: 'Alvin', topTwoFavorites: [ 'chocolate', 'cake' ] },
  { name: 'Tom', topTwoFavorites: [ 'donuts', 'pudding' ] },
  { name: 'Jessica', topTwoFavorites: [ 'fudge', 'smores' ] },
  { name: 'Rachel', topTwoFavorites: [ 'ice cream' ] }
]
```

在此範例中，運算`$slice`子用於從每個文件的`favorites`陣列中擷取前兩個元素。

## 程式碼範例
<a name="slice-code"></a>

若要檢視使用 `$slice`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('sweets');

  const result = await collection.aggregate([
    { $project: { name: 1, topTwoFavorites: { $slice: ['$favorites', 2] } } }
  ]).toArray();

  console.log(result);
  await 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['sweets']

    result = list(collection.aggregate([
        { '$project': { 'name': 1, 'topTwoFavorites': { '$slice': ['$favorites', 2] } } }
    ]))

    print(result)
    client.close()

example()
```

------