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Main performance tip is to find ways not to copy data generally:

- use .loc[]

- use inplace=True

can you elaborate on `using .loc[]` -- what is the defective approach it replaces?

I would assume using df[['colA', 'colB']] for projection/column selection?

Also, I would caution about using inplace=True. See: https://tomaugspurger.github.io/method-chaining.html (ctrl+F: "Inplace?")