Elixir Enum flat_map

Introduction

In Elixir, the Enum module provides a set of functions for working with enumerables. One such function is flat_map, which allows you to transform each element in an enumerable into a new enumerable and then flatten the result into a single enumerable.

This article will provide a comprehensive guide to understanding and using Enum.flat_map in Elixir. We will cover the syntax, usage examples, and discuss its usefulness in different scenarios.

Syntax

The syntax for using Enum.flat_map is as follows:

Enum.flat_map(collection, fun | key)

• collection is the enumerable or collection you want to iterate over.
• fun is a function or lambda that will be applied to each element in the collection.
• key is an optional argument that specifies a nested enumerable within each element of the collection.

Usage Examples

Example 1: Applying a function to each element

Let's say we have a list of numbers and we want to square each of them using Enum.flat_map:

numbers = [1, 2, 3, 4, 5]
squared_numbers = Enum.flat_map(numbers, fn(x) -> [x*x] end)

The fn(x) -> [x*x] end function will square each number in the numbers list and return a new list with the squared values. The result will be [1, 4, 9, 16, 25].

Example 2: Flattening a nested list

Suppose we have a list of lists and we want to flatten them using Enum.flat_map:

nested_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flattened_list = Enum.flat_map(nested_lists, fn(x) -> x end)

The function fn(x) -> x end is applied to each nested list, which effectively returns the original list as is. The result will be [1, 2, 3, 4, 5, 6, 7, 8, 9].

Example 3: Transforming nested elements

Let's consider a list of maps where each map has a nested list. We want to extract and flatten this nested list using Enum.flat_map:

people = [
  %{name: "John", hobbies: ["reading", "playing guitar"]},
  %{name: "Alice", hobbies: ["painting", "hiking"]}
]
hobbies = Enum.flat_map(people, fn(person) -> person[:hobbies] end)

The function fn(person) -> person[:hobbies] end selects the hobbies list from each person map. The result will be ["reading", "playing guitar", "painting", "hiking"].

Conclusion

The Enum.flat_map function in Elixir is a powerful tool for transforming and flattening enumerables. It allows you to apply a function to each element and collect the results in a single enumerable. Whether you need to apply a transformation or flatten nested enumerables, Enum.flat_map can simplify your code and make it more expressive.