---
title: "prefix(_:)"
framework: swift
role: symbol
role_heading: Instance Method
path: "swift/slice/prefix(_:)"
---

# prefix(_:)

Returns a subsequence, up to the specified maximum length, containing the initial elements of the collection.

## Declaration

```swift
func prefix(_ maxLength: Int) -> Self.SubSequence
```

## Parameters

- `maxLength`: The maximum number of elements to return. maxLength must be greater than or equal to zero.

## Return Value

Return Value A subsequence starting at the beginning of this collection with at most maxLength elements.

## Discussion

Discussion If the maximum length exceeds the number of elements in the collection, the result contains all the elements in the collection. let numbers = [1, 2, 3, 4, 5] print(numbers.prefix(2)) // Prints "[1, 2]" print(numbers.prefix(10)) // Prints "[1, 2, 3, 4, 5]" note: O(1) if the collection conforms to RandomAccessCollection; otherwise, O(k), where k is the number of elements to select from the beginning of the collection.