Github user falaki commented on a diff in the pull request:
https://github.com/apache/spark/pull/1025#discussion_r14688624
--- Diff:
core/src/test/scala/org/apache/spark/rdd/PairRDDFunctionsSuite.scala ---
@@ -83,6 +83,120 @@ class PairRDDFunctionsSuite extends FunSuite with
SharedSparkContext {
assert(valuesFor2.toList.sorted === List(1))
}
+ test("sampleByKey") {
+ def stratifier (fractionPositive: Double) = {
+ (x: Int) => if (x % 10 < (10 * fractionPositive).toInt) "1" else "0"
+ }
+
+ def checkSize(exact: Boolean, withReplacement: Boolean,
+ expected: Long, actual: Long, p: Double): Boolean = {
+ if (exact) {
+ return expected == actual
+ }
+ val stdev = if (withReplacement) math.sqrt(expected) else
math.sqrt(expected * p * (1 - p))
+ // Very forgiving margin since we're dealing with very small sample
sizes most of the time
+ math.abs(actual - expected) <= 6 * stdev
+ }
+
+ // Without replacement validation
+ def takeSampleAndValidateBernoulli(stratifiedData: RDD[(String, Int)],
+ exact: Boolean,
+ samplingRate: Double,
+ seed: Long,
+ n: Long) = {
+ val expectedSampleSize = stratifiedData.countByKey().mapValues(count
=>
+ math.ceil(count * samplingRate).toInt)
+ val fractions = Map("1" -> samplingRate, "0" -> samplingRate)
+ val sample = stratifiedData.sampleByKey(false, fractions, exact,
seed)
+ val sampleCounts = sample.countByKey()
+ val takeSample = sample.collect()
+ assert(sampleCounts.forall({case(k,v) =>
+ checkSize(exact, false, expectedSampleSize(k), v, samplingRate)}))
+ assert(takeSample.size === takeSample.toSet.size)
+ assert(takeSample.forall(x => 1 <= x._2 && x._2 <= n), s"elements
not in [1, $n]")
+ }
+
+ // With replacement validation
+ def takeSampleAndValidatePoisson(stratifiedData: RDD[(String, Int)],
+ exact: Boolean,
+ samplingRate: Double,
+ seed: Long,
+ n: Long) = {
+ val expectedSampleSize = stratifiedData.countByKey().mapValues(count
=>
+ math.ceil(count * samplingRate).toInt)
+ val fractions = Map("1" -> samplingRate, "0" -> samplingRate)
+ val sample = stratifiedData.sampleByKey(true, fractions, exact, seed)
+ val sampleCounts = sample.countByKey()
+ val takeSample = sample.collect()
+ assert(sampleCounts.forall({case(k,v) =>
+ checkSize(exact, true, expectedSampleSize(k), v, samplingRate)}))
+ val groupedByKey = takeSample.groupBy({case(k, v) => k})
--- End diff --
And here.
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