What is StringIndexer , VectorIndexer, and how to use them?
Dataset<Row> dataFrame = ... ;
StringIndexerModel labelIndexer = new StringIndexer()
.setInputCol("label")
.setOutputCol("indexedLabel")
.fit(dataFrame);
VectorIndexerModel featureIndexer = new VectorIndexer()
.setInputCol("s")
.setOutputCol("indexedFeatures")
.setMaxCategories(4)
.fit(dataFrame);
IndexToString labelConverter = new IndexToString()
.setInputCol("prediction")
.setOutputCol("predictedLabel")
.setLabels(labelIndexer.labels());