Kotlinized ChiSquareTestDemo (https://github.com/komiya-atsushi/dbflute-fes-2014-demo/blob/master/src/main/java/biz/k11i/demo/stat/ChiSquareTestDemo.java)

ChiSquareTestDemo.kt

package com.example

import org.apache.commons.math3.stat.inference.ChiSquareTest
import java.util.Random

/**
 * カイ二乗検定のデモ
 * https://github.com/komiya-atsushi/dbflute-fes-2014-demo/blob/master/src/main/java/biz/k11i/demo/stat/ChiSquareTestDemo.java
 * Kotlin ver
 */
fun main(args: Array<String>) {
    val rnd = SecureRandom()
    val times = 100000
    val alpha = 0.05
    rnd.run(rollFairDice(times))
        .let(doChiSqTest(alpha))
        .also(printChiSqTestResult("Fair Dice test", alpha))
    rnd.run(rollUnfairDice(times))
        .let(doChiSqTest(alpha))
        .also(printChiSqTestResult("Unfair Dice test", alpha))

}

private fun rollFairDice(times: Int): (Random) -> LongArray = { rnd ->
    LongArray(6).apply {
        for (i in 0 until times) {
            this[rnd.nextInt(6)]++
        }
    }
}

private fun rollUnfairDice(times: Int): (Random) -> LongArray = { rnd ->
    LongArray(6).apply {
        for (i in 0 until times) {
            this[if (i % 10 == 0) {
                0
            } else {
                rnd.nextInt(6)
            }]++
        }
    }
}

private fun doChiSqTest(alpha: Double): (LongArray) -> Pair<LongArray, Boolean> =
    { observed ->
        observed to ChiSquareTest().chiSquareTest(
            DoubleArray(6).apply { fill(1.0 / 6) },
            observed, alpha
        )
    }

private fun printChiSqTestResult(tag: String, alpha: Double): (Pair<LongArray, Boolean>) -> Unit =
    { (observed, isFitted) ->
        println( ("[%s]有意水準 %.3f%% での観測結果 %s のカイ二乗検定の結果は %s です。\n" +
                if (isFitted) "よって「さいころの各目が出る確率が等しい」という帰無仮説は棄却されます"
                else "よって「さいころの各目が出る確率が等しい」という帰無仮説は棄却されません").format(
            tag,
            alpha * 100,
            observed.contentToString(),
            isFitted
        ).let {
            if (isFitted) it.toAnsiRed() else it
        })
    }


const val ANSI_RED = "\u001B[31m"
const val ANSI_RESET = "\u001B[0m"
fun Any?.toAnsiRed() = ANSI_RED + this + ANSI_RESET