Array arithmetic in Ruby

I was digging around in some Rake source code this morning to learn about navigating file structure and ran down a rabbit hole of array math. I found some pretty neat things.

With Ruby#Array you can do something like the below:

ARRAY_METHODS = (Array.instance_methods - Object.instance_methods)

giving you the methods that are direct descendants of Array (and not inherited from Object). +1 for reading source code.

And back with the file traversal idea in mind I found a way to recursively list all the files in a directory without shipping out to the shell.

files_and_directories = Dir.glob("./test/**/*") # => Array
just_directories = Dir.glob("./test/**") # => Array
just_files = files_and_directories - just_directories # => Array of the
difference

These sorts of operations should have some pretty helpful applications when dealing with matrices, which I look forward to exploring more in the future.