Swift performance: map() and reduce() vs for loops

Question

I\'m writing some performance-critical code in Swift. After implementing all the optimizations I could think of, and profiling the application in Instruments, I came to rea

Answer 1

I did a quick set of performance tests measuring the performance of repeated transformations on an Array of Strings, and it showed that .map was much more performant than a for loop, by a factor of about 10x.

The results in the screenshot below show that chained transformations in a single map block outperform multiple maps with a single transformation in each, and any use of map out-performs for loops.

Code I used in a Playground:

import Foundation
import XCTest

class MapPerfTests: XCTestCase {
	var array =
		[
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString",
			"MyString"
	]

	func testForLoopAllInOnePerf() {
		measure {
			var newArray: [String] = []
			for item in array {
				newArray.append(item.uppercased().lowercased().uppercased().lowercased())
			}
		}
	}

	func testForLoopMultipleStagesPerf() {
		measure {
			var newArray: [String] = []
			for item in array {
				let t1 = item.uppercased()
				let t2 = item.lowercased()
				let t3 = item.uppercased()
				let t4 = item.lowercased()
				newArray.append(t4)
			}
		}
	}

	func testMultipleMapPerf() {
		measure {
			let newArray = array
				.map( { $0.uppercased() } )
				.map( { $0.lowercased() } )
				.map( { $0.uppercased() } )
				.map( { $0.lowercased() } )
		}
	}

	func testSingleMapPerf() {
		measure {
			let newArray = array
				.map( { $0.uppercased().lowercased().uppercased().lowercased() } )
		}
	}
}

MapPerfTests.defaultTestSuite.run()