如何使用Scala使用分类功能集运行Spark决策树?

问题描述

我有一个具有相应categoricalFeaturesInfo的要素集:Map [Int，Int].但是，对于我的一生，我无法弄清楚应该如何使DecisionTree类正常工作.它不接受任何内容，但接受LabeledPoint作为数据.但是，LabeledPoint需要(double，vector)，其中vector需要double.

I have a feature set with a corresponding categoricalFeaturesInfo: Map[Int,Int]. However, for the life of me I cannot figure out how I am supposed to get the DecisionTree class to work. It will not accept anything, but a LabeledPoint as data. However, LabeledPoint requires (double, vector) where the vector requires doubles.

val LP = featureSet.map(x => LabeledPoint(classMap(x(0)),Vectors.dense(x.tail)))

// Run training algorithm to build the model
val maxDepth: Int = 3
val isMulticlassWithCategoricalFeatures: Boolean = true
val numClassesForClassification: Int = countPossibilities(labelCol)
val model = DecisionTree.train(LP, Classification, Gini, isMulticlassWithCategoricalFeatures, maxDepth, numClassesForClassification,categoricalFeaturesInfo)

我得到的错误:

scala> val LP = featureSet.map(x => LabeledPoint(classMap(x(0)),Vectors.dense(x.tail)))
<console>:32: error: overloaded method value dense with alternatives:
  (values: Array[Double])org.apache.spark.mllib.linalg.Vector <and>
  (firstValue: Double,otherValues: Double*)org.apache.spark.mllib.linalg.Vector
 cannot be applied to (Array[String])
       val LP = featureSet.map(x => LabeledPoint(classMap(x(0)),Vectors.dense(x.tail)))

到目前为止，我的资源:树配置， 决策树， labeledpoint

My resources thus far:tree config, decision tree, labeledpoint

推荐答案

您可以先将类别转换为数字，然后像加载所有要素一样将其加载为数字.

You can first transform categories to numbers, then load data as if all features are numerical.

在Spark中构建决策树模型时，只需指定从特征索引到特征的映射Map[Int, Int]()，就可以告诉Spark哪些特征是分类的，以及特征的Arity(该特征的不同类别的数量)友善.

When you build a decision tree model in Spark, you just need to tell spark which features are categorical and also the feature's arity (the number of distinct categories of that feature) by specifying a map Map[Int, Int]() from feature indices to its arity.

例如，如果您的数据为:

For example if you have data as:

1,a,add
2,b,more
1,c,thinking
3,a,to
1,c,me

您可以先将数据转换为数字格式，如下所示:

You can first transform data into numerical format as:

1,0,0
2,1,1
1,2,2
3,0,3
1,2,4

您可以使用这种格式将数据加载到Spark.然后，如果您要告诉Spark第二列和第三列是分类的，则应创建一个地图:

In that format you can load data to Spark. Then if you want to tell Spark the second and the third columns are categorical, you should create a map:

categoricalFeaturesInfo = Map[Int, Int]((1,3),(2,5))

地图告诉我们索引1的特征具有3的特征，索引2的特征具有5的灵巧性.当我们构建将该地图作为训练函数的参数传递的决策树模型时，它们将被视为分类的:

The map tells us that feature with index 1 has arity 3, and feature with index 2 has artity 5. They will be considered as categorical when we build a decision tree model passing that map as a parameter of the training function:

val model = DecisionTree.trainClassifier(trainingData, numClasses, categoricalFeaturesInfo, impurity, maxDepth, maxBins)

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