Pipelines and Feature Unions

• FEATURE UNION: Feature union is a class in scikit-learn’s Pipeline module that allows us to perform steps in parallel and take the union of their results for the next step.
• A pipeline performs a list of steps in a linear sequence, while a feature union performs a list of steps in parallel and then combines their results.
• In more complex workflows, multiple feature unions are often used within pipelines, and multiple pipelines are used within feature unions.