Spark ML - What Is the Difference Between an Estimator and a Transformer?

Jason Kleski is a contributor to open source Spark and he's a very prolific writer online. If you want to know anything about Apache Spark, he's probably written something about it. And his books are also great resources. But I started to read through that like the design criteria of how these things worked. And it started to click a little bit more. Yeah, it's crazy what parallelizing can do. Never ceases to amaze.