In the previous lesson, you learned about some really handy enumerable methods like #each
, #map
, and #select
. In this lesson, we’re going to learn about even more enumerable methods! Woohoo! The party never ends here at The Odin Project!
This time, we’re focusing on a particular subset of enumerable methods: the predicate enumerable methods. You should recall from the Methods lesson that a predicate method is indicated by a question mark (?
) at the end of the method name and returns either true
or false
. Again, we won’t be going through all of the predicate enumerable methods, so be sure to have a look at the Ruby docs to see what else Enumerable offers.
For all of the examples throughout this lesson, feel free to follow along in irb or repl.it (an online REPL environment) to get a better feel for how they work.
By the end of this lesson, you should be able to do the following:
#include?
method works.#any?
method works.#all?
method works.#none?
method works.The #include?
method works exactly like you think it should. If we want to know whether a particular element exists in an array, we can use the #include?
method. This method will return true
if the element you pass as an argument to #include?
exists in the array or hash; otherwise, it will return false
.
First, let’s explore how we would achieve this with the #each
method:
numbers = [5, 6, 7, 8]
element = 6
result = false
numbers.each do |number|
if number == element
result = true
end
end
result
# => true
element = 3
result = false
numbers.each do |number|
if number == element
result = true
end
end
result
#=> false
Using #include?
, this code can be greatly simplified:
numbers = [5, 6, 7, 8]
numbers.include?(6)
#=> true
numbers.include?(3)
#=> false
For another example, let’s return to the friends
and invited_friends
arrays from the previous lesson:
friends = ['Sharon', 'Leo', 'Leila', 'Brian', 'Arun']
invited_list = friends.select { |friend| friend != 'Brian' }
invited_list.include?('Brian')
#=> false
You might also be able to guess what the #any?
method does. It returns true
if any elements in your array or hash match the condition within the block; otherwise, it will return false
.
Let’s say we want to see if there is any number greater than 500 or less than 20 in an array of numbers. First, let’s see how we could achieve this using #each
.
numbers = [21, 42, 303, 499, 550, 811]
result = false
numbers.each do |number|
if number > 500
result = true
end
end
result
#=> true
numbers = [21, 42, 303, 499, 550, 811]
result = false
numbers.each do |number|
if number < 20
result = true
end
end
result
#=> false
Using #any?
, this code can be greatly simplified:
numbers = [21, 42, 303, 499, 550, 811]
numbers.any? { |number| number > 500 }
#=> true
numbers.any? { |number| number < 20 }
#=> false
The all?
method is also fairly intuitive. It only returns true
if all the elements in your array or hash match the condition you set within the block; otherwise, it will return false
.
Let’s say that we want to check whether all the words in our list are more than 6 characters long. First,let’s see how we could achieve this using #each
:
fruits = ["apple", "banana", "strawberry", "pineapple"]
matches = []
result = false
fruits.each do |fruit|
if fruit.length > 3
matches.push(fruit)
end
result = fruits.length == matches.length
end
result
#=> true
fruits = ["apple", "banana", "strawberry", "pineapple"]
matches = []
result = false
fruits.each do |fruit|
if fruit.length > 6
matches.push(fruit)
end
result = fruits.length == matches.length
end
result
#=> false
Using #all?
, this code can be greatly simplified:
fruits = ["apple", "banana", "strawberry", "pineapple"]
fruits.all? { |fruit| fruit.length > 3 }
#=> true
fruits.all? { |fruit| fruit.length > 6 }
#=> false
Special note to keep in mind while debugging: #all?
will return true
by default unless the block returns false
or nil
. So if you call #all?
on an empty array or hash (i.e., there are no elements for the block to evaluate), it will return true
.
As you might expect, #none?
performs the opposite function of #all?
. It returns true
only if the condition in the block matches none of the elements in your array or hash; otherwise, it returns false
.
First, let’s see how this could be achieved using #each
. You’ll notice that this approach is very similar to what we did for #all?
.
fruits = ["apple", "banana", "strawberry", "pineapple"]
matches = []
result = false
fruits.each do |fruit|
if fruit.length > 10
matches.push(fruit)
end
result = matches.length == 0
end
result
#=> true
fruits = ["apple", "banana", "strawberry", "pineapple"]
matches = []
result = false
fruits.each do |fruit|
if fruit.length > 6
matches.push(fruit)
end
result = matches.length == 0
end
result
#=> false
Using #none?
, this can be greatly simplified:
fruits = ["apple", "banana", "strawberry", "pineapple"]
fruits.none? { |fruit| fruit.length > 10 }
#=> true
fruits.none? { |fruit| fruit.length > 6 }
#=> false
This section contains helpful links to other content. It isn’t required, so consider it supplemental for if you need to dive deeper into something.
#member?
and #one?
). For a full listing, you can check out the Ruby Docs.This section contains questions for you to check your understanding of this lesson. If you’re having trouble answering the questions below on your own, review the material above to find the answer.
#include?
method do?#any?
method do?#all?
method do?#none?
method do?5-6 months
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