Functional Programming Patterns in Scala and Clojure

Pattern 14

Filter-Map-Reduce

Intent

To manipulate a sequence (list, vector, and so on) declaratively using filter, map, and reduce to produce a new one—this is a powerful, high-level way of doing many sequence manipulations that would otherwise be verbose.

Overview

The way we manipulate sequences in a procedural language is more closely related to the way a computer works than to the way humans think. Iteration is a step above the dreaded goto statement, and it’s intended to be easily translated into machine code more than it’s intended to be easy to use.

Filter-Map-Reduce gives us a more declarative way to do many sequence manipulations. Instead of writing code that reorders or alters the elements in a sequence by working its way iteratively ...