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

# map(_:)

Returns an array containing the results of mapping the given closure over the sequence’s elements.

## Declaration

```swift
func map<T, E>(_ transform: (Self.Element) throws(E) -> T) throws(E) -> [T] where E : Error
```

## Parameters

- `transform`: A mapping closure. transform accepts an element of this sequence as its parameter and returns a transformed value of the same or of a different type.

## Return Value

Return Value An array containing the transformed elements of this sequence.

## Discussion

Discussion In this example, map is used first to convert the names in the array to lowercase strings and then to count their characters. let cast = ["Vivien", "Marlon", "Kim", "Karl"] let lowercaseNames = cast.map { $0.lowercased() } // 'lowercaseNames' == ["vivien", "marlon", "kim", "karl"] let letterCounts = cast.map { $0.count } // 'letterCounts' == [6, 6, 3, 4] note: O(n), where n is the length of the sequence.

## See Also

### Transforming a Sequence

- [compactMap(_:)](swift/sequence/compactmap(_:).md)
- [flatMap(_:)](swift/sequence/flatmap(_:)-jo2y.md)
- [reduce(_:_:)](swift/sequence/reduce(_:_:).md)
- [reduce(into:_:)](swift/sequence/reduce(into:_:).md)
- [lazy](swift/sequence/lazy.md)
- [flatMap(_:)](swift/sequence/flatmap(_:)-383uq.md)