Find/detect for first match in Ruby

Introduction

We use find or detect to quickly get the first item in a list that matches what we want. It saves time by stopping as soon as it finds a match.

Looking for the first person in a list who is older than 18.

Finding the first word in a sentence that starts with a capital letter.

Getting the first number in an array that is even.

Searching for the first file in a folder with a specific extension.

Syntax

Ruby

collection.find { |item| condition }
# or
collection.detect { |item| condition }

Both find and detect do the same thing in Ruby.

The block inside { } tells Ruby what condition to check for each item.

Examples

This finds the first even number in the list and prints it.

Ruby

numbers = [1, 3, 5, 8, 10]
even = numbers.find { |n| n.even? }
puts even

This finds the first word containing the letter 'a' and prints it.

Ruby

words = ['apple', 'banana', 'cherry']
word_with_a = words.detect { |w| w.include?('a') }
puts word_with_a

Sample Program

This program looks through a list of people and finds the first one who is 18 or older. Then it prints that person's name.

Ruby

people = [
  { name: 'Alice', age: 17 },
  { name: 'Bob', age: 20 },
  { name: 'Carol', age: 15 }
]
adult = people.find { |person| person[:age] >= 18 }
puts "First adult: #{adult[:name]}"

Important Notes

If no item matches, find returns nil.

You can use find with arrays, hashes, or any collection that supports iteration.

Summary

find and detect help you get the first matching item from a list.

They stop searching as soon as they find a match, making your code faster.

Use a block to tell Ruby what to look for in each item.