Brian Webb created SPARK-11581:
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Summary: Example mllib code in documentation incorrectly computes
MSE
Key: SPARK-11581
URL: https://issues.apache.org/jira/browse/SPARK-11581
Project: Spark
Issue Type: Bug
Components: Documentation
Affects Versions: 1.5.1
Reporter: Brian Webb
The example Java code at the bottom of the mllib-decision-tree web page shows
how to compute MSE on the test data. However, there is a bug in the code. The
code currently divides by data.count(), but it should instead divide by the
count of testData, testData.count().
http://spark.apache.org/docs/latest/mllib-decision-tree.html
Double testMSE =
predictionAndLabel.map(new Function<Tuple2<Double, Double>, Double>() {
@Override
public Double call(Tuple2<Double, Double> pl) {
Double diff = pl._1() - pl._2();
return diff * diff;
}
}).reduce(new Function2<Double, Double, Double>() {
@Override
public Double call(Double a, Double b) {
return a + b;
}
}) / data.count();
System.out.println("Test Mean Squared Error: " + testMSE);
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