Set-difference Questions

I created in stata a list of all files in a folder with the following: global file_all : dir "$outputsfolder" files

I encountered the below peculiar behaviour when creating difference of string sets in python: set(['a', 'b']) - set(['a']) #

I have two dataframes, say df1 and df2, with the same column names. example: df1 c1 | c2

What is the difference between difference() and symmetric_difference() methods in python sets?

I am working quite a bit with maps in javascript. i need the most computationally efficient way to find all items that are in map a that are not