python - 如何将稀疏数据的PythonRDD转换为密集的PythonRDD

Question

我想使用StandardScaler来缩放数据。我已将数据加载到 PythonRDD 中。看起来数据很稀疏。要应用StandardScaler，我们应该首先将其转换为密集类型。

trainData = MLUtils.loadLibSVMFile(sc, trainDataPath)
valData = MLUtils.loadLibSVMFile(sc, valDataPath) 
trainLabel = trainData.map(lambda x: x.label)
trainFeatures = trainData.map(lambda x: x.features)
valLabel = valData.map(lambda x: x.label)
valFeatures = valData.map(lambda x: x.features)
scaler = StandardScaler(withMean=True, withStd=True).fit(trainFeatures)

# apply the scaler into the data. Here, trainFeatures is a sparse PythonRDD, we first convert it into dense tpye
trainFeatures_scaled = scaler.transform(trainFeatures)
valFeatures_scaled = scaler.transform(valFeatures)    

# merge `trainLabel` and `traiFeatures_scaled` into a new PythonRDD
trainData1 = ...
valData1 = ...

# using the scaled data, i.e., trainData1 and valData1 to train a model
...

上面的代码有错误。我有两个问题:

1. 如何将稀疏的 PythonRDD trainFeatures 转换为密集的 tpye，作为 StandardScaler 的输入？
2. 如何将 trainLabel 和 trainFeatures_scaled 合并到可用于训练分类器(例如随机森林)的新 LabeledPoint 中？

我仍然找到有关此的任何文档或引用资料。

Answer 1

使用toArray转换为密集 map :

dense = valFeatures.map(lambda v: DenseVector(v.toArray()))

合并 zip:

valLabel.zip(dense).map(lambda (l, f): LabeledPoint(l, f))