---
title: "Ruby 2.4 adds Enumerable#uniq & Enumerable::Lazy#uniq"
description:
  "In Ruby 2.4, uniq elements can be iterated upon for enumerable and lazy
  objects without creating an array."
canonical_url: "https://www.bigbinary.com/blog/enumerable-uniq-and-enumerable-lazy-uniq-part-of-ruby-2-4"
markdown_url: "https://www.bigbinary.com/blog/enumerable-uniq-and-enumerable-lazy-uniq-part-of-ruby-2-4.md"
---

# Ruby 2.4 adds Enumerable#uniq & Enumerable::Lazy#uniq

In Ruby 2.4, uniq elements can be iterated upon for enumerable and lazy objects
without creating an array.

- Author: Mohit Natoo
- Published: March 21, 2017
- Categories: Ruby 2.4, Ruby

In Ruby, we commonly use `uniq` method on an array to fetch the collection of
all unique elements. But there may be cases where we might need elements in a
hash by virtue of uniqueness of its values.

Let's consider an example of countries that have hosted the Olympics. We only
want to know when was the first time a country hosted it.

```ruby

# given object
{ 1896 => 'Athens',
  1900 => 'Paris',
  1904 => 'Chicago',
  1906 => 'Athens',
  1908 => 'Rome' }

# expected outcome
{ 1896 => 'Athens',
  1900 => 'Paris',
  1904 => 'Chicago',
  1908 => 'Rome' }

```

One way to achieve this is to have a collection of unique country names and then
check if that value is already taken while building the result.

```ruby

olympics =
{ 1896 => 'Athens',
  1900 => 'Paris',
  1904 => 'Chicago',
  1906 => 'Athens',
  1908 => 'Rome' }

unique_nations = olympics.values.uniq

olympics.select{ |year, country| !unique_nations.delete(country).nil? }
#=> {1896=>"Athens", 1900=>"Paris", 1904=>"Chicago", 1908=>"Rome"}

```

As we can see, the above code requires constructing an additional array
`unique_nations`.

In processing larger data, loading an array of considerably big size in memory
and then carrying out further processing on it, may result in performance and
memory issues.

In Ruby 2.4, `Enumerable` class introduces `uniq`
[method](https://bugs.ruby-lang.org/issues/11090) that collects unique elements
while iterating over the enumerable object.

The usage is similar to that of Array#uniq. Uniqueness can be determined by the
elements themselves or by a value yielded by the block passed to the `uniq`
method.

```ruby

olympics = {1896 => 'Athens', 1900 => 'Paris', 1904 => 'Chicago', 1906 => 'Athens', 1908 => 'Rome'}

olympics.uniq { |year, country| country }.to_h
#=> {1896=>"Athens", 1900=>"Paris", 1904=>"Chicago", 1908=>"Rome"}

```

Similar method is also implemented in `Enumerable::Lazy` class. Hence we can now
call `uniq` on lazy enumerables.

```ruby

(1..Float::INFINITY).lazy.uniq { |x| (x**2) % 10 }.first(6)
#=> [1, 2, 3, 4, 5, 10]

```

## Links

- [Human page](https://www.bigbinary.com/blog/enumerable-uniq-and-enumerable-lazy-uniq-part-of-ruby-2-4)