Enumerators in Ruby

Enumerators are a set of methods to traverse, search, sort and manipulate collections (Lists and Hashes) in Ruby.

The concepts regarding enumerators are directly related with loops and collections. If you understand the concepts of loops, lists and hashes, there is absolutely nothing new conceptually in this post. Usually, Enumerators allow us to write more elegant solutions with fewer lines of code.

EACH

The Each method yields each element from the collection that is calling it to the block passed as argument. This method returns the original version collection, no mater what operations you applied to each element.

colors = ['blue', 'green', 'yellow', 'orange', 'red']

colors.each { |color| puts color.capitalize }

# Blue
# Green
# Yellow
# Orange
# Red
# => ["blue", "green", "yellow", "orange", "red"]

MAP

The Map method yields each element from the collection that is calling it to the block passed as argument. This method returns the modified version of the collection.

fruits = ['banana', 'apple', 'orange', 'grape', 'pear']

fruits.map { |fruit| fruit.upcase }

# => ["BANANA", "APPLE", "ORANGE", "GRAPE", "PEAR"]

COLLECT

The Collect method is just an alias for the Map method.

fruits = ['banana', 'apple', 'orange', 'grape', 'pear']

fruits.collect { |fruit| fruit.upcase }

# => ["BANANA", "APPLE", "ORANGE", "GRAPE", "PEAR"]

INJECT

The Inject method takes an accumulator (sum in the example below) and iterate through each element doing operations with them. This method returns the accumulator when it is done. In the example below we use the accumulator to hold the sum of all elements of the shopping_cart list.

shopping_cart = [9.0, 9.95, 5.9, 10.90, 3.20]

shopping_cart.inject { |sum, price| sum += price }

# => 38.95

REDUCE

The Reduce method is just an alias for the Inject method. We can also pass an initial value for the accumulator, default is 0.

shopping_cart = [9.0, 9.95, 5.9, 10.90, 3.20]

shopping_cart.reduce(10) { |sum, price| sum += price }

# => 48.95

SELECT

The Select method returns a list with all elements that matches the condition passed in the block. In this example it is going to return a list with all even numbers from the list.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers.select { |number| number.even? }

# => [2, 4, 6, 8, 10]

REJECT

The Reject method is exactly the opposite of the method Select; It returns a list with all elements that does not match the condition passed in the block. In the example below it is going to return a list with all odd numbers from the list. We are rejecting all the even numbers.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers.reject { |number| number.even? }

# => [1, 3, 5, 7, 9]

FIND

The Find method returns the first element in the collection that matches the condition passed in the block. It returns nil if there is no element that matches the condition.

names = ["Joseph", "Paul", "Pablo", "Mary", "Kristy"]

names.find { |name| name == "Pablo" }

# => "Pablo"

DETECT

The Detect method is just an alias for the Find method.

names = ["Joseph", "Paul", "Pablo", "Mary", "Kristy"]

names.detect { |name| name == "Patrick" }

# => nil

Enumerators are a great feature in the Ruby language. It makes it easier to work with collections. I hope you liked this post and I am looking forward to writing the next one.