Flat_map for nested flattening in Ruby

Introduction

Flat_map helps you turn a list of lists into a single list by combining all inner lists into one. It makes nested data easier to work with.

You have a list of groups and want one list of all items.

You want to simplify nested arrays into a flat array.

You want to apply a transformation and flatten the result in one step.

You want to avoid writing extra loops to flatten nested data.

Syntax

Ruby

array.flat_map { |element| block }

The block returns an array for each element.

flat_map combines all returned arrays into one flat array.

Examples

Flattens the nested arrays into one array: [1, 2, 3, 4]

Ruby

[[1, 2], [3, 4]].flat_map { |a| a }

For each number, creates an array with the number and its double, then flattens: [1, 2, 2, 4, 3, 6]

Ruby

[1, 2, 3].flat_map { |n| [n, n * 2] }

Sample Program

This program takes a nested list of fruits and vegetables and flattens it into one list.

Ruby

nested = [["apple", "banana"], ["carrot", "date"], ["egg"]]
flat = nested.flat_map { |group| group }
puts flat.inspect

Important Notes

flat_map is like map followed by flatten(1), but faster and cleaner.

Use flat_map when your block returns arrays and you want one flat array.

If your block returns single values, flat_map works like map.

Summary

flat_map flattens one level of nested arrays after mapping.

It simplifies working with nested lists by combining mapping and flattening.

Use it to get a single list from nested lists easily.