spark决策树API分析

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输入

Param name	Type(s)	Default	Description
labelCol	Double	“label”	标签
featuresCol	Vector	“features”	特征向量

输出

Param name	Type(s)	Default	Description	Notes
predictionCol	Double	“prediction”	预测结果标签
rawPredictionCol	Vector	“rawPrediction”	Vector of length # classes, with the counts of training instance labels at the tree node which makes the prediction	仅限分类
probabilityCol	Vector	“probability”	Vector of length # classes equal to rawPrediction normalized to a multinomial distribution	仅限分类
varianceCol	Double		预测结果方差	仅限回归

API函数

决策树分类器
class pyspark.ml.classification.DecisionTreeClassifier(self, featuresCol=”features”, labelCol=”label”, predictionCol=”prediction”, probabilityCol=”probability”, rawPredictionCol=”rawPrediction”, maxDepth=5, maxBins=32, minInstancesPerNode=1, minInfoGain=0.0, maxMemoryInMB=256, cacheNodeIds=False, checkpointInterval=10, impurity=”gini”)

maxDepth=5表示树的深度最大为5

maxBins=32表示离散化连续变量分区个数最大值

imputity=”gini”决策树节点特征选择方式，类似还有c45等

代码实例

>>> from pyspark.mllib.linalg import Vectors
>>> from pyspark.ml.feature import StringIndexer
>>> df = sqlContext.createDataFrame([
...     (1.0, Vectors.dense(1.0)),
...     (0.0, Vectors.sparse(1, [], []))], ["label", "features"])
>>> stringIndexer = StringIndexer(inputCol="label", outputCol="indexed")
>>> si_model = stringIndexer.fit(df)
>>> td = si_model.transform(df)
>>> dt = DecisionTreeClassifier(maxDepth=2, labelCol="indexed")
>>> model = dt.fit(td)
>>> model.numNodes
3
>>> model.depth
1
>>> test0 = sqlContext.createDataFrame([(Vectors.dense(-1.0),)], ["features"])
>>> result = model.transform(test0).head()
>>> result.prediction
0.0
>>> result.probability
DenseVector([1.0, 0.0])
>>> result.rawPrediction
DenseVector([1.0, 0.0])
>>> test1 = sqlContext.createDataFrame([(Vectors.sparse(1, [0], [1.0]),)], ["features"])
>>> model.transform(test1).head().prediction
1.0

决策树模型

class pyspark.ml.classification.DecisionTreeClassificationModel(java_model)

模型是通过决策树分类器训练获得

主要的内部成员函数是transform，负责对测试样本预测分类，返回结果是dataframe格式
transform(dataset, params=None)

Transforms the input dataset with optional parameters.

Parameters:	dataset – input dataset, which is an instance of `pyspark.sql.DataFrame` params – an optional param map that overrides embedded params.
Returns:	transformed dataset