我在Apache Spark ML(版本1.5.1)中使用NaiveBayes分类器来预测某些文本类别 . 但是,分类器输出的标签与我的训练集中的标签不同 . 我做错了吗?
这是一个可以粘贴到例如Zeppelin笔记本:
import org.apache.spark.ml.Pipeline
import org.apache.spark.ml.classification.NaiveBayes
import org.apache.spark.ml.feature.{HashingTF, Tokenizer}
import org.apache.spark.mllib.linalg.Vector
import org.apache.spark.sql.Row
// Prepare training documents from a list of (id, text, label) tuples.
val training = sqlContext.createDataFrame(Seq(
(0L, "X totally sucks :-(", 100.0),
(1L, "Today was kind of meh", 200.0),
(2L, "I'm so happy :-)", 300.0)
)).toDF("id", "text", "label")
// Configure an ML pipeline, which consists of three stages: tokenizer, hashingTF, and lr.
val tokenizer = new Tokenizer()
.setInputCol("text")
.setOutputCol("words")
val hashingTF = new HashingTF()
.setNumFeatures(1000)
.setInputCol(tokenizer.getOutputCol)
.setOutputCol("features")
val nb = new NaiveBayes()
val pipeline = new Pipeline()
.setStages(Array(tokenizer, hashingTF, nb))
// Fit the pipeline to training documents.
val model = pipeline.fit(training)
// Prepare test documents, which are unlabeled (id, text) tuples.
val test = sqlContext.createDataFrame(Seq(
(4L, "roller coasters are fun :-)"),
(5L, "i burned my bacon :-("),
(6L, "the movie is kind of meh")
)).toDF("id", "text")
// Make predictions on test documents.
model.transform(test)
.select("id", "text", "prediction")
.collect()
.foreach { case Row(id: Long, text: String, prediction: Double) =>
println(s"($id, $text) --> prediction=$prediction")
}
小程序的输出:
(4, roller coasters are fun :-)) --> prediction=2.0
(5, i burned my bacon :-() --> prediction=0.0
(6, the movie is kind of meh) --> prediction=1.0
预测标签{0.0,1.0,2.0}的集合与我的训练集标签{100.0,200.0,300.0}不相交 .
问题:如何将这些预测标签映射回原始训练集标签?
奖金问题:为什么训练集标签必须是双打,当任何其他类型的标签和标签一样好?似乎没必要 .
1 回答
的种类 . 据我所知,你正在达到SPARK-9137描述的问题 . 一般来说,ML中的所有分类器都期望基于0的标签(0.0,1.0,2.0,...),但
ml.NaiveBayes
中没有验证步骤 . 引擎盖下的数据传递给mllib.NaiveBayes
,但没有这个限制,因此训练过程顺利进行 .当模型转换回
ml
时,预测函数只是假设标签正确,并且returns predicted label using Vector.argmax,因此得到的结果 . 您可以使用例如StringIndexer
来修复标签 .我想这主要是保持简单和可重用的API . 这样
LabeledPoint
可以用于分类和回归问题 . 此外,它在内存使用和计算成本方面是一种有效的表示 .