Compare 2 Hash with values consisting of array

Question

I have 2 hashes, let's say A, B

A: { 'key1' => [a, b], 'key2' => 'c' }
B: { 'key1' => [b, a], 'key2' => 'c' }

What is the best possible way to compare these 2 hashes. The ordering of the array contents does not matter. So in my case, hash A and B are equal

Answer 1

I came up with this solution:

def are_equals?(a, b)
  (a.keys.sort == b.keys.sort) &&
  a.merge(b) { |k, o_val, n_val| [o_val, n_val].all? { |e| e.kind_of? Array} ? o_val.sort == n_val.sort : o_val == n_val }.values.all?
end

---

How it works.

The first part tests for key equality, using Hash#keys, which returns the array of keys, sorted of course:

a.keys.sort == b.keys.sort

For the second part I used Hash#merge to compare values related to the same key, and can be expanded in this way:

res = a.merge(b) do |k, o_val, n_val|
  if [o_val, n_val].all? { |e| e.kind_of? Array}
    o_val.sort == n_val.sort
  else
    o_val == n_val
  end
end

#=> {"key1"=>true, "key2"=>true}

It returns a Hash where values are true or false, then checks if all values are true using Enumerable#all?:

res.values.all?
#=> [true, true].all? => true

Answer 2

I would definitely agree with Ivan it's not as easy as it initially seems but I figured I would try doing it with recursion. This has the added benefit of being able to compare beyond just hashes.

hash_a = {'key1' => ['a', 'b'], 'key2' => 'c'}
hash_b = {'key1' => ['b', 'a'], 'key2' => 'c'}
hash_c = {'key1' => ['a', 'c'], 'key2' => 'c'}
hash_d = {'key1' => ['a', 'b'], 'key2' => 'd'}
hash_e = {'key1' => ['a', 'b'], 'key2' => ['a', 'b']}
hash_f = {'key1' => ['a', 'b'], 'key2' => 'c', 'key3' => 'd'}


def recursive_compare(one, two)
  unless one.class == two.class
    return false
  end

  match = false

  # If it's not an Array or Hash...
  unless one.class == Hash || one.class == Array
    return one == two
  end

  # If they're both Hashes...
  if one.class == Hash
    one.each_key do |k|
      match = two.key? k
      break unless match
    end

    two.each_key do |k|
      match = one.key? k
      break unless match
    end

    if match
      one.each do |k, v|
        match = recursive_compare(v, two[k])
        break unless match
      end
    end
  end

  # If they're both Arrays...
  if one.class == Array
    one.each do |v|
      match = two.include? v
      break unless match
    end
    two.each do |v|
      match = one.include? v
      break unless match
    end
  end

  match
end

puts recursive_compare(hash_a, hash_b) #=> true
puts recursive_compare(hash_a, hash_c) #=> false
puts recursive_compare(hash_a, hash_d) #=> false
puts recursive_compare(hash_a, hash_e) #=> false
puts recursive_compare(hash_a, hash_f) #=> false

Answer 3

One can sort the arrays but that can be an expensive operation if the arrays are large. If n equals the size of the array, the time complexity of heapsort, for example, is O(n log(n)). It's faster to replace arrays with counting hashes, the construction of which enjoys a time complexity of O(n).

h1 = { 'k1' => [1, 2, 1, 3, 2, 1], 'k2' => 'c' }
h2 = { 'k1' => [3, 2, 1, 2, 1, 1], 'k2' => 'c' }

def same?(h1, h2)
  return false unless h1.size == h2.size
  h1.all? do |k,v|
    if h2.key?(k)
      vo = h2[k]
      if v.is_a?(Array)
        if vo.is_a?(Array) 
          convert(v) == convert(vo)
        end
      else
        v == vo
      end
    end
  end
end           

def convert(arr)
  arr.each_with_object(Hash.new(0)) { |e,g| g[e] += 1 }
end

same?(h1, h2)
  #=> true

Here

convert([1, 2, 1, 3, 2, 1])
  #=> {1=>3, 2=>2, 3=>1} 
convert([3, 2, 1, 2, 1, 1])
  #=> {3=>1, 2=>2, 1=>3}

and

{1=>3, 2=>2, 3=>1} == {3=>1, 2=>2, 1=>3}
  #=> true

See Hash::new, specifically the case where the method takes an argument that equals the default value.

The guard clause return false unless h1.size == h2.size is to ensure that h2 does not have keys that are not present in h1. Note that the following returns the falsy value nil:

if false
  #...
end
  #=> nil

In a couple of places I've written that rather than the more verbose but equivalent expresion

if false
  #...
else
  nil
end

Answer 4

It's not as easy as it seems at first glance.
It is necessary to take into account several nuances:

• the number of elements in the hashes may not match;
• items with the same key in two hashes can be of different types.

A relatively universal solution can be as follows:

def hashes_comp(hash1, hash2)
  return false if hash1.size != hash2.size
  hash1.each do |key, value|
    if value.class == Array
      return false if hash2[key].class != Array || value.sort != hash2[key].sort
    else
      return false if value != hash2[key]
    end
  end
  true
end

hash_a = {'key1' => ['a', 'b'], 'key2' => 'c'}
hash_b = {'key1' => ['b', 'a'], 'key2' => 'c'}
hash_c = {'key1' => ['a', 'c'], 'key2' => 'c'}
hash_d = {'key1' => ['a', 'b'], 'key2' => 'd'}
hash_e = {'key1' => ['a', 'b'], 'key2' => ['a', 'b']}
hash_f = {'key1' => ['a', 'b'], 'key2' => 'c', 'key3' => 'd'}

hashes_comp(hash_a, hash_b) #=> true
hashes_comp(hash_a, hash_c) #=> false
hashes_comp(hash_a, hash_d) #=> false
hashes_comp(hash_a, hash_e) #=> false
hashes_comp(hash_a, hash_f) #=> false