Compare performance reduce to joined & map+joined

map-joined-reduce.swift

/** 
  Measuring the performance of reduce compared to joined and map+joined.
  Spoiler: map+joined way more faster!!!
  Try this code in a .playground file if you want.
  */

func measure(closure: (()->Void)) {
    let start = Date()
    closure()
    let interval = Date().timeIntervalSince(start)
    print(interval)
}

// joined vs. reduce

let nested: [[UInt8]] = Array(repeating: Array(repeating: 200, count: 100), count: 100)

// 0.00224500894546509 sec
measure {
    _ = nested.joined()
}

// 1.02885299921036 sec
measure {
    _ = nested.reduce([]) { $0 + $1 }
}

// map + joined vs. reduce

let values: [UInt8] = Array(repeating: 200, count: 10000)

// 0.34653902053833 sec
measure {
    _ = values.map{"\($0)"}.joined()
}

// 16.6465470194817 sec
measure {
    _ = values.reduce("") {
        return "\($0)\($1)"
    }
}

// map + joined with separator vs. reduce

// 0.499653995037079 sec
measure {
    _ = values.map{"\($0)"}.joined(separator: ".")
}

// 22.2956600189209 sec
measure {
    _ = values.reduce("") {
        return $0 + ($0.isEmpty ? "" : ".") + "\($1)"
    }
}

// Results: map+joined burnt reduce
// 0.00224500894546509 vs 1.02885299921036
// 0.34653902053833 vs 16.6465470194817
// 0.499653995037079 vs 22.2956600189209