ちょっと Kotlin の Iterator と Sequence の比較をしてみた

benchmarkIteratorAndSequence.kt

import kotlin.system.measureNanoTime

fun buildUseList(list: List<Int>, half: Int): List<String> {
    return list
        .filter { it < half }
        .filter { it % 2 == 0 }
        .map { it.toString() }
        .take(3)
}

fun buildUseSequence(list: List<Int>, half: Int): List<String> {
    return list
        .asSequence()
        .filter { it < half }
        .filter { it % 2 == 0 }
        .map { it.toString() }
        .take(3)
        .toList()
}

fun main() {
    val dataSet =
        listOf(1_000_000, 100_000, 10_000, 1_000, 200, 100, 10)
            .associateWith { (1..it).toList() }

    // warmup
    val warm = 1_000_000 to (1..1_000_000).toList()
    buildUseList(warm.second, warm.first / 2)
    buildUseSequence(warm.second, warm.first / 2)
    // end of warmup

    dataSet.forEach {
        println("useList     %8d %8d nsec".format(it.key, measureNanoTime { buildUseList(it.value, it.key / 2) }))
        println("useSequence %8d %8d nsec".format(it.key, measureNanoTime { buildUseSequence(it.value, it.key / 2) }))
    }
}

output on Android

検証した Android 端末
Pixel 3 XL / Android 10 (ART)

2020-01-11 22:51:03.871 18459-18459/com.sample.app001 I/System.out: useList      1000000 162565537 nsec
2020-01-11 22:51:03.871 18459-18459/com.sample.app001 I/System.out: useSequence  1000000   116718 nsec
2020-01-11 22:51:03.883 18459-18459/com.sample.app001 I/System.out: useList       100000 11641147 nsec
2020-01-11 22:51:03.884 18459-18459/com.sample.app001 I/System.out: useSequence   100000   102969 nsec
2020-01-11 22:51:03.885 18459-18459/com.sample.app001 I/System.out: useList        10000  1226875 nsec
2020-01-11 22:51:03.886 18459-18459/com.sample.app001 I/System.out: useSequence    10000   116875 nsec
2020-01-11 22:51:03.886 18459-18459/com.sample.app001 I/System.out: useList         1000   166250 nsec
2020-01-11 22:51:03.886 18459-18459/com.sample.app001 I/System.out: useSequence     1000    64271 nsec
2020-01-11 22:51:03.887 18459-18459/com.sample.app001 I/System.out: useList          200    54948 nsec
2020-01-11 22:51:03.887 18459-18459/com.sample.app001 I/System.out: useSequence      200    63177 nsec
2020-01-11 22:51:03.887 18459-18459/com.sample.app001 I/System.out: useList          100    49688 nsec
2020-01-11 22:51:03.887 18459-18459/com.sample.app001 I/System.out: useSequence      100    62604 nsec
2020-01-11 22:51:03.888 18459-18459/com.sample.app001 I/System.out: useList           10    42448 nsec
2020-01-11 22:51:03.888 18459-18459/com.sample.app001 I/System.out: useSequence       10    60364 nsec

output on Hotspot(?)

検証したマシン/Java 環境
macOS Catalina / Intel Core i9 2.9 GHz / 32GB
OpenJDK Runtime Environment Corretto-11.0.5.10.2 (build 11.0.5+10-LTS)

useList      1000000 60066750 nsec
useSequence  1000000    28238 nsec
useList       100000  1507380 nsec
useSequence   100000    23472 nsec
useList        10000   130913 nsec
useSequence    10000    43383 nsec
useList         1000    20584 nsec
useSequence     1000    17550 nsec
useList          200     8385 nsec
useSequence      200    16703 nsec
useList          100     6814 nsec
useSequence      100    16689 nsec
useList           10    15051 nsec
useSequence       10    28847 nsec