spark 针对决策树进行交叉验证
from pyspark import SparkContext, SQLContext from pyspark.ml import Pipeline from pyspark.ml.classification import DecisionTreeClassifier from pyspark.ml.feature import StringIndexer, VectorIndexer from pyspark.ml.evaluation import MulticlassClassificationEvaluator # Load the data stored in LIBSVM format as a DataFrame. data = sqlContext.read.format("libsvm").load("data/mllib/sample_libsvm_data.txt") # Index labels, adding metadata to the label column. # Fit on whole dataset to include all labels in index. labelIndexer = StringIndexer(inputCol="label", outputCol="indexedLabel").fit(data) # Automatically identify categorical features, and index them. # We specify maxCategories so features with > 4 distinct values are treated as continuous. featureIndexer =\ VectorIndexer(inputCol="features", outputCol="indexedFeatures", maxCategories=4).fit(data) # Split the data into training and test sets (30% held out for testing) (trainingData, testData) = data.randomSplit([0.7, 0.3]) # Train a DecisionTree model. dt = DecisionTreeClassifier(labelCol="indexedLabel", featuresCol="indexedFeatures") # Chain indexers and tree in a Pipeline pipeline = Pipeline(stages=[labelIndexer, featureIndexer, dt]) # Train model. This also runs the indexers. model = pipeline.fit(trainingData) # Make predictions. predictions = model.transform(testData) # Select example rows to display. predictions.select("prediction", "indexedLabel", "features").show(5) # Select (prediction, true label) and compute test error evaluator = MulticlassClassificationEvaluator( labelCol="indexedLabel", predictionCol="prediction", metricName="precision") accuracy = evaluator.evaluate(predictions) print("Test Error = %g " % (1.0 - accuracy)) treeModel = model.stages[2] # summary only print(treeModel) ############################# from pyspark.ml.tuning import ParamGridBuilder, CrossValidator # Create ParamGrid for Cross Validation paramGrid = (ParamGridBuilder() .addGrid(lr.regParam, [0.01, 0.5, 2.0]) .addGrid(lr.elasticNetParam, [0.0, 0.5, 1.0]) .addGrid(lr.maxIter, [1, 5, 10]) .build()) Copy to clipboardCopy # Create 5-fold CrossValidator cv = CrossValidator(estimator=lr, estimatorParamMaps=paramGrid, evaluator=evaluator, numFolds=5) # Run cross validations cvModel = cv.fit(trainingData) # this will likely take a fair amount of time because of the amount of models that we're creating and testing # Use test set here so we can measure the accuracy of our model on new data predictions = cvModel.transform(testData) # cvModel uses the best model found from the Cross Validation # Evaluate best model evaluator.evaluate(predictions) #We can also access the model’s feature weights and intercepts easily print 'Model Intercept: ', cvModel.bestModel.intercept ML provides CrossValidator class which can be used to perform cross-validation and parameter search. Assuming your data is already preprocessed you can add cross-validation as follows: import org.apache.spark.ml.Pipeline import org.apache.spark.ml.tuning.{ParamGridBuilder, CrossValidator} import org.apache.spark.ml.classification.RandomForestClassifier import org.apache.spark.ml.evaluation.MulticlassClassificationEvaluator // [label: double, features: vector] trainingData org.apache.spark.sql.DataFrame = ??? val nFolds: Int = ??? val NumTrees: Int = ??? val metric: String = ??? val rf = new RandomForestClassifier() .setLabelCol("label") .setFeaturesCol("features") .setNumTrees(NumTrees) val pipeline = new Pipeline().setStages(Array(rf)) val paramGrid = new ParamGridBuilder().build() // No parameter search val evaluator = new MulticlassClassificationEvaluator() .setLabelCol("label") .setPredictionCol("prediction") // "f1" (default), "weightedPrecision", "weightedRecall", "accuracy" .setMetricName(metric) val cv = new CrossValidator() // ml.Pipeline with ml.classification.RandomForestClassifier .setEstimator(pipeline) // ml.evaluation.MulticlassClassificationEvaluator .setEvaluator(evaluator) .setEstimatorParamMaps(paramGrid) .setNumFolds(nFolds) val model = cv.fit(trainingData) // trainingData: DataFrame Using PySpark: from pyspark.ml import Pipeline from pyspark.ml.classification import RandomForestClassifier from pyspark.ml.tuning import CrossValidator, ParamGridBuilder from pyspark.ml.evaluation import MulticlassClassificationEvaluator trainingData = ... # DataFrame[label: double, features: vector] numFolds = ... # Integer rf = RandomForestClassifier(labelCol="label", featuresCol="features") evaluator = MulticlassClassificationEvaluator() # + other params as in Scala pipeline = Pipeline(stages=[rf]) crossval = CrossValidator( estimator=pipeline, estimatorParamMaps=paramGrid, evaluator=evaluator, numFolds=numFolds) model = crossval.fit(trainingData) 本文转自张昺华-sky博客园博客，原文链接：http://www.cnblogs.com/bonelee/p/7803849.html，如需转载请自行联系原作者
