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From mengxr <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-2082] stratified sampling in PairRDDFun...
Date Wed, 09 Jul 2014 05:47:27 GMT
Github user mengxr commented on a diff in the pull request:

    https://github.com/apache/spark/pull/1025#discussion_r14694380
  
    --- Diff: core/src/test/scala/org/apache/spark/rdd/PairRDDFunctionsSuite.scala ---
    @@ -83,6 +83,125 @@ 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) =>
    --- End diff --
    
    Put spaces after `{` and `,`.
    
    Better put assert inside foreach so we can output more info if something goes wrong.


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