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.
Delete
A delete filter is expressed via a predicate. A predicate is developed as a function or operator that returns a boolean.