Map, Filter, Reduce in Swift

With Swift, iOS and Mac developers have map, filter, and reduce methods on arrays. These methods can replace almost all uses of for-in-loops, and are more clear and concise.

map_filter_reduce.swift    Select all

let words = ["angry", "hungry", "aardvark", "aardwolf"] func concatenate(xs: [String]) -> String { var result: String = "" for x in xs { result += x + " " } return result.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet()) } concatenate(words) // "angry hungry aardvark aardwolf" println("GRR!! " + words .filter {$0.hasSuffix("gry")} .map {$0.uppercaseString} .reduce("HULK") {"\($0) \($1)"} + "!!!" ) // "GRR!! HULK ANGRY HUNGRY!!!" let numbers = [ 10000, 10303, 30913, 50000, 100000, 101039, 1000000 ] println( numbers .filter { $0 % 2 == 0 } .map { NSNumberFormatter.localizedStringFromNumber($0, numberStyle: .DecimalStyle) } .reduce("") { countElements($0) == 0 ? $1 : $0 + " " + $1 } ) // "10,000 50,000 100,000 1,000

Updated for Swift 3.0 syntax below

map_filter_reduce.swift    Select all

let words = ["angry", "hungry", "aardvark", "aardwolf"] func concatenate(_ xs: [String]) -> String { var result: String = "" for x in xs { result += x + " " } return result.trimmingCharacters(in: .whitespaces) // Xcode 8 beta 6 // return result.trimmingCharacters(in: NSCharacterSet.whitespaces()) // Xcode 8 beta 1 } concatenate(words) // "angry hungry aardvark aardwolf" print("GRR!! " + words .filter {$0.hasSuffix("gry")} .map {$0.uppercased()} .reduce("HULK") {"\($0) \($1)"} + "!!!" ) // "GRR!! HULK ANGRY HUNGRY!!!" let numbers = [ 10000, 10303, 30913, 50000, 100000, 101039, 1000000 ] print( numbers .filter { $0 % 2 == 0 } .map { NumberFormatter.localizedString(from: ($0 as NSNumber) , number: .decimal) } // Xcode 8 beta 6 // .map { NumberFormatter.localizedString(from: $0, number: .decimal) } //Xcode 8 beta 1 .reduce("") { $0.characters.count == 0 ? $1 : $0 + " " + $1 } ) // "10,000 50,000 100,000 1,000