Spark ML 中的维度不匹配错误

Question

我对 ML 和 Spark ML 都很陌生，我正在尝试使用带有 Spark ML 的神经网络制作预测模型，但是当我.transform在我学习的模型上调用方法时出现此错误。问题是由使用 OneHotEncoder 引起的，因为没有它一切正常。我曾尝试将 OneHotEncoder 带出管道。

我的问题是：如何使用 OneHotEncoder 而不会出现此错误？

 java.lang.IllegalArgumentException: requirement failed: A & B Dimension mismatch! 
 at scala.Predef$.require(Predef.scala:224)     at org.apache.spark.ml.ann.BreezeUtil$.dgemm(BreezeUtil.scala:41)   at
 org.apache.spark.ml.ann.AffineLayerModel.eval(Layer.scala:163)     at
 org.apache.spark.ml.ann.FeedForwardModel.forward(Layer.scala:482)  at
 org.apache.spark.ml.ann.FeedForwardModel.predict(Layer.scala:529)

我的代码：

test_pandas_df = pd.read_csv(
    '/home/piotrek/ml/adults/adult.test', names=header, skipinitialspace=True)
train_pandas_df = pd.read_csv(
    '/home/piotrek/ml/adults/adult.data', names=header, skipinitialspace=True)
train_df = sqlContext.createDataFrame(train_pandas_df)
test_df = sqlContext.createDataFrame(test_pandas_df)

joined = train_df.union(test_df)

assembler = VectorAssembler().setInputCols(features).setOutputCol("features")

label_indexer = StringIndexer().setInputCol(
    "label").setOutputCol("label_index")

label_indexer_fit = [label_indexer.fit(joined)]

string_indexers = [StringIndexer().setInputCol(
    name).setOutputCol(name + "_index").fit(joined) for name in categorical_feats]

one_hot_pipeline = Pipeline().setStages([OneHotEncoder().setInputCol(
    name + '_index').setOutputCol(name + '_one_hot') for name in categorical_feats])

mlp = MultilayerPerceptronClassifier().setLabelCol(label_indexer.getOutputCol()).setFeaturesCol(
    assembler.getOutputCol()).setLayers([len(features), 20, 10, 2]).setSeed(42L).setBlockSize(1000).setMaxIter(500)
pipeline = Pipeline().setStages(label_indexer_fit
                                + string_indexers + [one_hot_pipeline] + [assembler, mlp])

model = pipeline.fit(train_df)

# compute accuracy on the test set
result = model.transform(test_df)

## FAILS ON RESULT

predictionAndLabels = result.select("prediction", "label_index")

evaluator = MulticlassClassificationEvaluator(labelCol="label_index")
print "-------------------------------"
print("Test set accuracy = " + str(evaluator.evaluate(predictionAndLabels)))
print "-------------------------------"

谢谢！

Answer 1

layers Param 在您的模型中不正确：

setLayers([len(features), 20, 10, 2])

第一层应反映输入特征的数量，通常与编码前的原始列数不同。

如果您事先不知道特征的总数，您可以例如将特征提取和模型训练分开。伪代码：

feature_pipeline_model = (Pipeline()
     .setStages(...)  # Only feature extraction
     .fit(train_df))

train_df_features = feature_pipeline_model.transform(train_df)
layers = [
    train_df_features.schema["features"].metadata["ml_attr"]["num_attrs"],
    20, 10, 2
]