title: pyspark: easiest way to save and read an RDD
body: <p>In pyspark, what would be the easiest way to save a RDD as a file, so later on I can read the file back as an RDD?</p>
  
  <p>I saw a lot of save method such as saveAsPickle, saveAsSequence,  saveAsObject ... etc. But not much mentioning about how to read these files back to an RDD. Please advise.</p>
  
  <p>Thanks!</p>