Intro to Python for Computer Science and Data Science: Learning to Program with AI, Big Data and The Cloud

5.14 Filter, Map and Reduce

The preceding section introduced several functional-style features—list comprehensions, filtering and mapping. Here we demonstrate the built-in filter and map functions for filtering and mapping, respectively. We continue discussing reductions in which you process a collection of elements into a single value, such as their count, total, product, average, minimum or maximum.

Filtering a Sequence’s Values with the Built-In filter Function

Let’s use built-in function filter to obtain the odd values in numbers:

In [1]: numbers = [10, 3, 7, 1, 9, 4, 2, 8, 5, 6]

In [2]: def is_odd(x):
   ...:     """Returns True only if x is odd."""
   ...:     return x % 2 != 0
   ...:

In [3]: list(filter(is_odd, numbers))
Out[3]: [3, 7, 1, 9, 5]