apache/spark — pull request #2296 by davies (2014-09-05 23:06:51+00:00)
Title: [SPARK-2334] fix AttributeError when call PipelineRDD.id()

The underline JavaRDD for PipelineRDD is created lazily, it's delayed until call _jrdd.

The id of JavaRDD is cached as `_id`, it saves a RPC call in py4j for later calls.