Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/14551#discussion_r74005725
--- Diff: core/src/test/scala/org/apache/spark/util/UtilsSuite.scala ---
@@ -874,4 +874,38 @@ class UtilsSuite extends SparkFunSuite with
ResetSystemProperties with Logging {
}
}
}
+
+ test("chi square test of randomizeInPlace") {
+ // Parameters
+ val arraySize = 10
+ val numTrials = 1000
+ val threshold = 0.05
+ val seed = 1L
+
+ // results[i][j]: how many times Utils.randomize moves an element from
position j to position i
+ val results: Array[Array[Long]] = Array.ofDim(arraySize, arraySize)
+
+ // This must be seeded because even a fair random process will fail
this test with
+ // probability equal to the value of `threshold`, which is
inconvenient for a unit test.
+ val rand = new java.util.Random(seed)
+ val range = 0 until arraySize
+
+ for {
+ _ <- 0 until numTrials
+ trial = Utils.randomizeInPlace(range.toArray, rand)
+ i <- range
+ } results(i)(trial(i)) += 1L
+
+ val chi = new org.apache.commons.math3.stat.inference.ChiSquareTest()
+
+ // We expect an even distribution; this array will be rescaled by
`chiSquareTest`
+ val expected: Array[Double] = Array.fill(arraySize * arraySize)(1.0)
+ val observed: Array[Long] = results.flatMap(x => x)
--- End diff --
`flatten`?
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