About

filtering is a data processing operation that processes data through a filter where the data may be:

• deleted according to a predicate from a collection
• transformed (map operation)

Therefore, you need to be careful about what filter means. For instance:

• In the OS shell, a shell filter is a transformation operation
• In functional programming or SQL, a functional programming filter is a delete operation
• In the SMTP world, a email filter is a transformation operation known as a milter.