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

The `$slice` update operator modifies an array by limiting its size. When used with the `$push` operator, it restricts the number of elements in an array, keeping only the specified number of most recent or oldest elements.

**Parameters**
+ `field`: The array field to modify.
+ `count`: Maximum number of elements to keep. Positive values keep the first N elements, negative values keep the last N elements.

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

The following example demonstrates how to use the `$slice` update operator with `$push` to maintain a fixed-size array of recent scores.

**Create sample documents**

```
db.students.insertOne({
  _id: 1,
  name: "Alice",
  scores: [85, 90, 78]
});
```

**Query example**

```
db.students.updateOne(
  { _id: 1 },
  {
    $push: {
      scores: {
        $each: [92, 88],
        $slice: -3
      }
    }
  }
)
```

**Output**

```
{
  "_id" : 1,
  "name" : "Alice",
  "scores" : [ 78, 92, 88 ]
}
```

In this example, the `$slice: -3` modifier keeps only the last three elements after pushing new values to the array.

## Code examples
<a name="slice-update-code"></a>

To view a code example for using the `$slice` update operator, choose the tab for the language that you want to use:

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

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

async function updateDocument() {
  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('students');

  await collection.updateOne(
    { _id: 1 },
    {
      $push: {
        scores: {
          $each: [92, 88],
          $slice: -3
        }
      }
    }
  );

  const updatedDocument = await collection.findOne({ _id: 1 });
  console.log(updatedDocument);

  await client.close();
}

updateDocument();
```

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

```
from pymongo import MongoClient

def update_document():
    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.students

    collection.update_one(
        {'_id': 1},
        {
            '$push': {
                'scores': {
                    '$each': [92, 88],
                    '$slice': -3
                }
            }
        }
    )

    updated_document = collection.find_one({'_id': 1})
    print(updated_document)

    client.close()

update_document()
```

------