What I really like to do for this is loading it into SQLite, there are built in macros for reading/writing CSV files. And they're queryable with SQL which makes for a great jumping point to do some basic cleaning, joining and analysis.

This also I'd argue makes the job easier with LLMs since you can ask it to write a SQL query which you can validate / reason about rather than relying on it for transforming the data itself (which I've seen a lot under this post)