[SPARK-21681][ML] fix bug of MLOR do not work correctly when featureStd contains zero (backport PR for 2.2)

mllib/src/main/scala/org/apache/spark/ml/classification/LogisticRegression.scala

@@ -1727,11 +1727,13 @@ private class LogisticAggregator(
 
     val margins = new Array[Double](numClasses)
     features.foreachActive { (index, value) =>
-      val stdValue = value / localFeaturesStd(index)
-      var j = 0
-      while (j < numClasses) {
-        margins(j) += localCoefficients(index * numClasses + j) * stdValue
-        j += 1
+      if (localFeaturesStd(index) != 0.0 && value != 0.0) {
+        val stdValue = value / localFeaturesStd(index)
+        var j = 0
+        while (j < numClasses) {
+          margins(j) += localCoefficients(index * numClasses + j) * stdValue
+          j += 1
+        }
       }
     }
     var i = 0

mllib/src/test/scala/org/apache/spark/ml/classification/LogisticRegressionSuite.scala

@@ -45,6 +45,7 @@ class LogisticRegressionSuite
   @transient var smallMultinomialDataset: Dataset[_] = _
   @transient var binaryDataset: Dataset[_] = _
   @transient var multinomialDataset: Dataset[_] = _
+  @transient var multinomialDatasetWithZeroVar: Dataset[_] = _
   private val eps: Double = 1e-5
 
   override def beforeAll(): Unit = {
@@ -98,6 +99,23 @@ class LogisticRegressionSuite
       df.cache()
       df
     }
+
+    multinomialDatasetWithZeroVar = {
+      val nPoints = 100
+      val coefficients = Array(
+        -0.57997, 0.912083, -0.371077,
+        -0.16624, -0.84355, -0.048509)
+
+      val xMean = Array(5.843, 3.0)
+      val xVariance = Array(0.6856, 0.0)
+
+      val testData = generateMultinomialLogisticInput(
+        coefficients, xMean, xVariance, addIntercept = true, nPoints, seed)
+
+      val df = sc.parallelize(testData, 4).toDF().withColumn("weight", lit(1.0))
+      df.cache()
+      df
+    }
   }
 
   /**
@@ -111,6 +129,11 @@ class LogisticRegressionSuite
     multinomialDataset.rdd.map { case Row(label: Double, features: Vector, weight: Double) =>
       label + "," + weight + "," + features.toArray.mkString(",")
     }.repartition(1).saveAsTextFile("target/tmp/LogisticRegressionSuite/multinomialDataset")
+    multinomialDatasetWithZeroVar.rdd.map {
+      case Row(label: Double, features: Vector, weight: Double) =>
+        label + "," + weight + "," + features.toArray.mkString(",")
+    }.repartition(1)
+      .saveAsTextFile("target/tmp/LogisticRegressionSuite/multinomialDatasetWithZeroVar")
   }
 
   test("params") {
@@ -1391,6 +1414,58 @@ class LogisticRegressionSuite
     assert(model2.interceptVector.toArray.sum ~== 0.0 absTol eps)
   }
 
+  test("multinomial logistic regression with zero variance (SPARK-21681)") {
+    val sqlContext = multinomialDatasetWithZeroVar.sqlContext
+    import sqlContext.implicits._
+    val mlr = new LogisticRegression().setFamily("multinomial").setFitIntercept(true)
+      .setElasticNetParam(0.0).setRegParam(0.0).setStandardization(true).setWeightCol("weight")
+
+    val model = mlr.fit(multinomialDatasetWithZeroVar)
+
+    /*
+     Use the following R code to load the data and train the model using glmnet package.
+     library("glmnet")
+     data <- read.csv("path", header=FALSE)
+     label = as.factor(data$V1)
+     w = data$V2
+     features = as.matrix(data.frame(data$V3, data$V4))
+     coefficients = coef(glmnet(features, label, weights=w, family="multinomial",
+     alpha = 0, lambda = 0))
+     coefficients
+     $`0`
+     3 x 1 sparse Matrix of class "dgCMatrix"
+                    s0
+             0.2658824
+     data.V3 0.1881871
+     data.V4 .
+     $`1`
+     3 x 1 sparse Matrix of class "dgCMatrix"
+                      s0
+              0.53604701
+     data.V3 -0.02412645
+     data.V4  .
+     $`2`
+     3 x 1 sparse Matrix of class "dgCMatrix"
+                     s0
+             -0.8019294
+     data.V3 -0.1640607
+     data.V4  .
+    */
+
+    val coefficientsR = new DenseMatrix(3, 2, Array(
+      0.1881871, 0.0,
+      -0.02412645, 0.0,
+      -0.1640607, 0.0), isTransposed = true)
+    val interceptsR = Vectors.dense(0.2658824, 0.53604701, -0.8019294)
+
+    model.coefficientMatrix.colIter.foreach(v => assert(v.toArray.sum ~== 0.0 absTol eps))
+
+    assert(model.coefficientMatrix ~== coefficientsR relTol 0.05)
+    assert(model.coefficientMatrix.toArray.sum ~== 0.0 absTol eps)
+    assert(model.interceptVector ~== interceptsR relTol 0.05)
+    assert(model.interceptVector.toArray.sum ~== 0.0 absTol eps)
+  }
+
   test("multinomial logistic regression with intercept without regularization with bound") {
     // Bound constrained optimization with bound on one side.
     val lowerBoundsOnCoefficients = Matrices.dense(3, 4, Array.fill(12)(1.0))