我正在构建一个从Dataframe中提取功能的ml管道，我希望它的行为如下：
日志“提取特征1”
提取特征1
日志“提取特征2”
提取特征2
...
日志“提取特征n”
提取特征n
问题是，由于懒惰，我最终得出以下结论：
日志“提取特征1”
日志“提取特征2”
日志“提取特征n”
提取特征1
提取特征2
...
提取特征n
我的转换方法看起来有点像：

override def transform(dataset: DataFrame): DataFrame = {
   require(featuresToExtract.size > 0, "You must provide at least one feature to extract to use this FeatureExtractorTransformer")

   var joinedDataFrame = extract(dataset, featuresToExtract head)

   for (featureToExtract <- featuresToExtract.tail) {
     // LOGGING HERE THAT I WANT CALLED JUST BEFORE THE CORRESPONDING ACTION
     joinedDataFrame = joinedDataFrame.join(extract(dataset, featureToExtract), joinOn, "outer")
   }
   joinedDataFrame
}

你知道怎么做吗？
谢谢