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

# 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]