An overview of function varieties

We need to distinguish between two broad species of functions, as follows:

• Scalar functions apply to individual values and compute an individual result. Functions such as abs(), pow(), and the entire math module are examples of scalar functions.
• Collection() functions work with iterable collections.

We can further subdivide the collection functions into three subspecies:

• Reduction: This uses a function that is used to fold values in the collection together, resulting in a single final value. We can call this an aggregate function, as it produces a single aggregate value for an input collection.
• Mapping: This applies a function to all items of a collection; the result is a collection of the same size.
• Filter: This applies a function to all items of a collection that rejects some items and passes others. The result is a subset of the input. A filter might do nothing, which means that the output matches the input; this is an improper subset, but it still fits the...