Advantages of Set in ruby

Question

The main advantage of Set seems to be maintaining unique elements. But that can be easily achieved in Array with,

array = [2,3,4]
array | [2,5,6] # => [2,3,4,5,6]

The only distinct feature (which could apply to few use-cases) I came across was,

set1 = [1,2,3].to_set
set2 = [2,1,3].to_set
set1 == set2 # => true
[1,2,3] == [2,1,3] # => false

Since Array has various functions and operations associated with it, when and why should I use Set?

There are many links that compare Array and Set but I haven't come across significant application of Set.

Answer 1

For the obvious reasons, see the other answers here. For performance reasons, see the result of this little benchmark in MRI Ruby 1.9.3:

require 'benchmark' 
require 'set' 

array = (1..100000).to_a 
set = array.to_set 
#hash = Hash[array.map {|x| [x, nil]}] #beter voor heel grote volumes mar trager
hash = Hash[*array]

Benchmark.bmbm do |x| 
  x.report("Set.include?")   { 10000.times { set.include?(99999) } }
  x.report("Array.include?") { 10000.times { array.include?(99999) } } 
  x.report("Hash.include?")  { 10000.times { hash.include?(99999) } } 
end 

which gives

Rehearsal --------------------------------------------------
Set.include?     0.000000   0.000000   0.000000 (  0.015604)
Array.include?  37.940000   0.000000  37.940000 ( 38.651992)
Hash.include?    0.000000   0.000000   0.000000 (  0.001000)
---------------------------------------- total: 37.940000sec

                     user     system      total        real
Set.include?     0.000000   0.000000   0.000000 (  0.002001)
Array.include?  38.157000   0.000000  38.157000 ( 38.730615)
Hash.include?    0.000000   0.000000   0.000000 (  0.001001)

Enough reason to use Set or Hash when possible.