Recommendation for a good book on Spark, beginner to moderate knowledge

[Ashok Kumar]

  Hi Gurus,
Appreciate if you recommend me a good book on Spark or documentation for 
beginner to moderate knowledge
I very much like to skill myself on transformation and action methods.
FYI, I have already looked at examples on net. However, some of them not clear 
at least to me.
Warmest regards