我正在将Spark 1.5.1与MLLib一起使用。我使用MLLib建立了一个随机森林模型，现在使用该模型进行预测。我可以使用.predict函数找到预测类别（0.0或1.0）。但是，我找不到用于检索概率的函数（请参阅随附的屏幕截图）。我以为星火1.5.1随机森林会提供可能性，我在这里错过了什么吗？
最佳答案
不幸的是，该功能在较旧的Spark MLlib 1.5.1中不可用。
但是，您可以在Spark MLlib 2.x的最新管道API中以RandomForestClassifier的形式找到它：
import org.apache.spark.ml.Pipeline
import org.apache.spark.ml.classification.RandomForestClassifier
import org.apache.spark.ml.feature.{IndexToString, StringIndexer, VectorIndexer}
import org.apache.spark.mllib.util.MLUtils
// Load and parse the data file, converting it to a DataFrame.
val data = MLUtils.loadLibSVMFile(sc, "data/mllib/sample_libsvm_data.txt").toDF
// Index labels, adding metadata to the label column.
// Fit on whole dataset to include all labels in index.
val labelIndexer = new StringIndexer()
.setInputCol("label")
.setOutputCol("indexedLabel").fit(data)
// Automatically identify categorical features, and index them.
// Set maxCategories so features with > 4 distinct values are treated as continuous.
val featureIndexer = new VectorIndexer()
.setInputCol("features")
.setOutputCol("indexedFeatures")
.setMaxCategories(4).fit(data)
// Split the data into training and test sets (30% held out for testing)
val Array(trainingData, testData) = data.randomSplit(Array(0.7, 0.3))
// Train a RandomForest model.
val rf = new RandomForestClassifier()
.setLabelCol(labelIndexer.getOutputCol)
.setFeaturesCol(featureIndexer.getOutputCol)
.setNumTrees(10)
// Convert indexed labels back to original labels.
val labelConverter = new IndexToString()
.setInputCol("prediction")
.setOutputCol("predictedLabel")
.setLabels(labelIndexer.labels)
// Chain indexers and forest in a Pipeline
val pipeline = new Pipeline()
.setStages(Array(labelIndexer, featureIndexer, rf, labelConverter))
// Fit model. This also runs the indexers.
val model = pipeline.fit(trainingData)
// Make predictions.
val predictions = model.transform(testData)
// predictions: org.apache.spark.sql.DataFrame = [label: double, features: vector, indexedLabel: double, indexedFeatures: vector, rawPrediction: vector, probability: vector, prediction: double, predictedLabel: string]
predictions.show(10)
// +-----+--------------------+------------+--------------------+-------------+-----------+----------+--------------+
// |label| features|indexedLabel| indexedFeatures|rawPrediction|probability|prediction|predictedLabel|
// +-----+--------------------+------------+--------------------+-------------+-----------+----------+--------------+
// | 0.0|(692,[124,125,126...| 1.0|(692,[124,125,126...| [0.0,10.0]| [0.0,1.0]| 1.0| 0.0|
// | 0.0|(692,[124,125,126...| 1.0|(692,[124,125,126...| [1.0,9.0]| [0.1,0.9]| 1.0| 0.0|
// | 0.0|(692,[129,130,131...| 1.0|(692,[129,130,131...| [1.0,9.0]| [0.1,0.9]| 1.0| 0.0|
// | 0.0|(692,[154,155,156...| 1.0|(692,[154,155,156...| [1.0,9.0]| [0.1,0.9]| 1.0| 0.0|
// | 0.0|(692,[154,155,156...| 1.0|(692,[154,155,156...| [1.0,9.0]| [0.1,0.9]| 1.0| 0.0|
// | 0.0|(692,[181,182,183...| 1.0|(692,[181,182,183...| [1.0,9.0]| [0.1,0.9]| 1.0| 0.0|
// | 1.0|(692,[99,100,101,...| 0.0|(692,[99,100,101,...| [4.0,6.0]| [0.4,0.6]| 1.0| 0.0|
// | 1.0|(692,[123,124,125...| 0.0|(692,[123,124,125...| [10.0,0.0]| [1.0,0.0]| 0.0| 1.0|
// | 1.0|(692,[124,125,126...| 0.0|(692,[124,125,126...| [10.0,0.0]| [1.0,0.0]| 0.0| 1.0|
// | 1.0|(692,[125,126,127...| 0.0|(692,[125,126,127...| [10.0,0.0]| [1.0,0.0]| 0.0| 1.0|
// +-----+--------------------+------------+--------------------+-------------+-----------+----------+--------------+
// only showing top 10 rows
注意：此示例来自Spark MLlib的ML - Random forest classifier的官方文档。
这是一些输出列的一些解释：
predictionCol代表预测的标签。rawPredictionCol表示一个长度为＃类的Vector，在进行预测的树节点上有训练实例标签的计数（仅适用于分类）。probabilityCol表示长度＃类的概率向量，其等于归一化为多项分布的rawPrediction（仅适用于分类）。