Summarizing a collection – how to reduce
A reduction is the generalized concept behind computing a sum or a product of a collection of numbers. Computing statistical measures like mean or variance are also reductions. In this recipe, we'll look at several summary techniques.
In the introduction to this chapter, we noted that there are three processing patterns that Python supports elegantly: map, filter, and reduce. We saw examples of mapping in the Applying transformations to a collection recipe and examples of filtering in the Picking a subset – three ways to filter recipe. It's relatively easy to see how these higher-level functions define generic operations.
The third common pattern is reduction. In the Designing classes with lots of processing and Extending a collection: a list that does statistics recipes, we looked at class definitions that computed a number of statistical values. These definitions relied—almost exclusively—on the...
