Reject for inverse filtering in Ruby

Introduction

Rejecting items helps you remove unwanted things from a list based on a rule. Inverse filtering means keeping only those items that do NOT match the rule.

When you want to remove all even numbers from a list and keep only odd numbers.

When you want to filter out all words that contain a certain letter.

When you want to exclude all users under 18 years old from a list.

When you want to remove all empty strings from a list of words.

Syntax

Ruby

array.reject { |item| condition }

The block inside reject returns true for items to remove.

Reject returns a new array without the rejected items.

Examples

Removes even numbers, keeps odd numbers.

Ruby

numbers = [1, 2, 3, 4, 5]
odd_numbers = numbers.reject { |n| n.even? }
puts odd_numbers.inspect

Removes words containing letter 'a'.

Ruby

words = ['apple', 'banana', 'pear']
no_a = words.reject { |w| w.include?('a') }
puts no_a.inspect

Sample Program

This program removes fruits that contain the letter 'a' and shows both lists.

Ruby

fruits = ['apple', 'banana', 'cherry', 'date']
# Remove fruits that have the letter 'a'
filtered = fruits.reject { |fruit| fruit.include?('a') }
puts "Original: #{fruits.inspect}"
puts "Filtered: #{filtered.inspect}"

Important Notes

Reject is the opposite of select, which keeps items matching the condition.

Reject does not change the original array unless you use reject! with an exclamation mark.

Summary

Use reject to remove items matching a condition.

It returns a new array without those items.

Great for filtering out unwanted elements easily.