How to Use Ruby Any, All, None & One

Today you’ll learn about 4 Enumerable methods that will help you check a conditional statement against an array of elements, a hash, or any other objects that include the Enumerable module.

Ruby Any, All, None, One Methods

These 4 methods return either true or false.

Contents

Let’s do this!

Ruby All Method

If you want to check if all the strings inside an array have a specific size.

You could do this:

def all_words_have_specific_size?(words)
  return false if words.empty?

  words.each do |str|
    return false unless str.size == 5
  end

  true
end

words = ["bacon", "orange", "apple"]

all_words_have_specific_size?(words)
# false

We check every string, if the size isn’t what we want we return false, otherwise we return true at the end.

That’s a lot of code for something like this.

Imagine having to set this up every time you want to do this kind of check.

It’s a lot of work!

The only thing we care about here is this:

str.size == 5

That’s the condition we are checking.

Is there a better way to do this?

Yes!

Use the all? method to do all the hard work for you.

Here’s how:

strings.all? { |str| str.size == 5 }

That’s it.

All & Empty Arrays

One thing you must know:

This all? method will return true if you call it on an empty array.

Example:

[].all? { |s| s.size == 1 }
# true

Explanation:

Since NO elements are false then all elements must be true.

That’s the logic behind this.

Ruby None Method

If you want the reverse of all?, use none?

Here’s an example:

strings.none? { |str| str.size == 5 }

This returns true if none of the strings match the condition, or false if one or more match it.

It’s like unless for if statements.

Ruby Any Method

Would you like to know if ANY element matches your condition?

You can use the any? method!

Like this:

[1,2,3,4,5].any?
# true

In this specific example, any? works like the inverse of empty?. But that won’t work for every situation.

Because this is asking the question:

“Are there any TRUTHY elements inside this array?”

If your array includes only non-truthy (nil/false) values you’ll get false, but the array is not really empty.

Example:

[nil].any?
# false

You can also pass a block to this method:

[1,2,3].any? { |n| n > 0 }
# true

This will check if n > 0 is true for AT LEAST one element.

Ruby One Method

You can check if EXACTLY one element returns true with the one? method.

Here’s an example:

["a", 1, {}].one? { |obj| obj.kind_of?(Hash) }
# true

You can use this without a block to check if the array contains exactly one truthy value (anything but false / nil).

["a"].one?
# true

[].one?
# false

[nil].one?
# false

I will stick to size == 1 because it’s more explicit. Everyone will understand that even if they aren’t familiar with the one? method, which is not that common.

New Ruby 2.5 Feature

Since Ruby 2.5 these 4 methods (any? / all? / none? / one?) also take an argument which works like grep’s argument.

Here’s what I mean:

[:orange, :apple, :coconut].any?(Symbol)
# true

[1,2,3].all?(1..10)
# true

This is a nice little shortcut if you want to check for a class, regular expression or a range.

Summary

You have learned about 4 awesome Ruby methods that can save you a lot of work! These methods only return either true or false.

If you haven’t used these methods before… why not give them a try now?

Please share this article if you found it useful.

2 comments
Dave Aronson says 4 years ago

Just to pile on: a lot of people think that .any? checks if an enumerable contains any elements, and .none? checks if there are no elements (like .empty?). There’s a nasty gotcha lurking in that interpretation.

These don’t check whether elements exist, but whether they make the block return a truthy value (or if you don’t pass a block, then whether they are truthy). So frex [nil, false].any? is false, and [nil, false].none? is true.

    Jesus Castello says 4 years ago

    Thanks for you comment Dave!

Comments are closed