What are some must-know Spark functions? I know this is a pretty granular question, but what are some must-know Spark, specifically PySpark, functions for a data engineer? I need to brush up on it for an interview and after having not used it for a full year, I've admittedly forgotten a lot of it. And thinking about it, I didn't use it very extensively, so my knowledge about Spark is coming up short.

I can do I/O fairly easily, but I'm looking for data-wrangling functions that any data engineer should know. Not sure if I'll have access to documentation during the interview