Map/collect for transformation in Ruby

Introduction

Map (also called collect) helps you change each item in a list to something new, making a new list with these changed items.

When you want to add 1 to every number in a list.

When you want to turn a list of names into a list of greetings.

When you want to get the length of each word in a list.

When you want to change all temperatures from Celsius to Fahrenheit.

When you want to make all words uppercase in a list.

Syntax

Ruby

new_array = old_array.map { |item| transformation }

You can also use 'collect' instead of 'map'; they do the same thing.

The block inside curly braces { } tells Ruby how to change each item.

Examples

Multiply each number by 2.

Ruby

numbers = [1, 2, 3]
doubled = numbers.map { |n| n * 2 }
# doubled is [2, 4, 6]

Get the length of each word.

Ruby

words = ["cat", "dog"]
lengths = words.map { |w| w.length }
# lengths is [3, 3]

Make a greeting for each name.

Ruby

names = ["Alice", "Bob"]
greetings = names.map { |name| "Hello, #{name}!" }
# greetings is ["Hello, Alice!", "Hello, Bob!"]

Sample Program

This program changes all fruit names to uppercase and prints the new list.

Ruby

fruits = ["apple", "banana", "cherry"]
uppercase_fruits = fruits.map { |fruit| fruit.upcase }
puts uppercase_fruits

Important Notes

Map does not change the original list; it makes a new one.

You can use map with any kind of list, like numbers, words, or objects.

If you want to change the original list, use map! with an exclamation mark.

Summary

Map/collect changes each item in a list and returns a new list.

Use a block to tell Ruby how to change each item.

Original list stays the same unless you use map!.