We need to distinguish between two broad species of functions, as follows:
We can further subdivide the collection functions into three subspecies:
- Reduction: This uses a function to fold values in the collection together, resulting in a single final value. For example, if we fold (
+
) operations into a sequence of integers, this will compute the sum. This can be also be called an aggregate function, as it produces a single aggregate value for an input collection. - Mapping: This applies a scalar function to each individual item of a collection; the result is a collection of the same size.
- Filter: This applies a scalar function to all items of a collection to reject some items and pass others. The result is a subset of the input.
We...