Set vs Array , difference

Question

What is the difference between Set and Array in Ruby except for the fact that sets keep unique elements while arrays can keep duplicate elements?

Solution 1

They are very different.

Array

• An array is an ordered list of objects.
• An array value can be accessed by referencing its integer position in the list (zero-indexed): a[3] references the 4th object in the array.
• There is no restriction on what the values can be—duplicate values are allowed in arrays.
• An array has an object literal notation: [1, 'apple', String, 1, :banana] (this creates and initializes a new Array).
• Arrays are built in to the core ruby library.

Set

• A set is an unordered pool of unique objects.
• Since it's unordered, there is no integer index you can use to access specific elements of a set.
• The uniqueness restriction means you can't have more than one copy of a value in the set.
• Set is not part of the core, but part of the standard library, and thus needs a require 'set'.
• Before Ruby 2.4, there was no object literal notation for sets, you had to create them via Set.new.
  • For Ruby >= 2.4.0 you can use Set[] (e.g. Set[1,2,3])

Solution 2

For me the main difference is that Sets are implemented as hashes, so you have O(1) membership tests for elements.

Solution 3

Another important difference is in the implementation of the include? method: an Array compares members based on the result of the == method, while a Set uses the eql? method.

Comments

[Bhushan Lodha]

this link may give you more fruitful insight on this topic.

[Clint Pachl]

Set.new.class.superclass #=> Object

[Clint Pachl]

$ ri Set.eql? states: "For objects of class Object, eql? is synonymous with ==."

[user1678401]

Most sets and arrays do not contain objects of class Object. They contain objects of a subclass of Object, of which there are many for which eql? and == are not synonymous.

[Sampson Crowley]

There is a literal notation now (as of ruby 2.4): Set[1,2,3]