Enumerable Examples - Part 1

enumerable_example_p1.md

Enumerable Examples

Enumerable is a mixin that is used to add additional functionality to collection classes like Array and Hash. This means that you can use the methods defined in Enumerable on both arrays and hashes.

#map

Enumberable#map is useful when you want to create a new array by iterating over some collection of values, and calculate a new value based on each item in the collection.

We might want to create a new array by iterating over an array of integers, adding 100 to each value.

One way to do this without using map is to use #each:

numbers = [1, 2, 3, 4]
bigger_numbers = []

numbers.each do |number|
  bigger_numbers << number + 100
end

bigger_numbers
# => [101, 102, 103, 104]

This can be simplified by using #map:

numbers = [1, 2, 3, 4]

bigger_numbers = numbers.map do |number|
  number + 100
end

# => [101, 102, 103, 104]

A new array will be created using the result of each iteration through the numbers array.

#sort

Enumerable#sort is great when you want to sort an array of strings alphabetically:

people = ['Eric', 'Adam', 'Richard', 'Helen']

sorted_people = people.sort

# => ["Adam", "Eric", "Helen", "Richard"]

Or sort an array of integers by their value:

numbers = [1, 15, 2, 4, 17]

sorted_numbers = numbers.sort

# => [1, 2, 4, 15, 17]

#sort_by

Enumerable#sort_by is great when you want to sort by a more complicated value.

Here's an example where we sort an array of hashes where each hash represents a person. We can use #sort_by to sort the array by each person's last name:

people = [
  { first_name: 'Eric', last_name: 'Kelly' },
  { first_name: 'Adam', last_name: 'Sheehan' },
  { first_name: 'Richard', last_name: 'Davis' },
  { first_name: 'Helen', last_name: 'Hood' }
]

sorted_people = people.sort_by do |person|
  person[:last_name]
end

# => [
#  {:first_name=>"Richard", :last_name=>"Davis"},
#  {:first_name=>"Helen", :last_name=>"Hood"},
#  {:first_name=>"Eric", :last_name=>"Kelly"},
#  {:first_name=>"Adam", :last_name=>"Sheehan"}
# ]

#find

Enumerable#find is useful for searching for specific items within a collection.

Imagine we have an array of hashes, each representing a person. We can find the person with a given first name using #find:

people = [
  { first_name: 'Eric', last_name: 'Kelly' },
  { first_name: 'Adam', last_name: 'Sheehan' },
  { first_name: 'Richard', last_name: 'Davis' },
  { first_name: 'Helen', last_name: 'Hood' }
]

richard = people.find do |person|
  person[:first_name] == 'Richard'
end

# => {:first_name=>"Richard", :last_name=>"Davis"}

In the previous example, the #find method will iterate over each person hash until it finds one where the first name is 'Richard'.

#find_all

Enumerable#find_all, like #find, is useful for searching for specific items within a collection. The difference is that #find is only going to return the first item that matches the given conditions. #find_all is going to return an array containing all of the matching items in the collection.

For example, we can find all of the people with the first name Richard:

people = [
  { first_name: 'Eric', last_name: 'Kelly' },
  { first_name: 'Adam', last_name: 'Sheehan' },
  { first_name: 'Richard', last_name: 'Davis' },
  { first_name: 'Helen', last_name: 'Hood' },
  { first_name: 'Richard', last_name: 'Simmons' }
]

all_the_richards = people.find_all do |person|
  person[:first_name] == 'Richard'
end

# => [
#  {:first_name=>"Richard", :last_name=>"Davis"},
#  {:first_name=>"Richard", :last_name=>"Simmons"}
# ]