CODEWITHSUNDEEP
ruby
abhijit
abhijit

Reputation: 6703

Search an Array of Hashes with a partial Hash in Ruby

Given a hash 

z = [{'a' => 1, 'b' => 2}, {'a' => 3, 'b' => 4}, {'a' => 1, 'b' => 4}]

How do I search if the search parameter itself is a hash e.g. 

{'a' => 3}

so that I can do something like z.find_by_hash({'a' => 3}) for it to return 

{'a' => 3, 'b' => 4}

and also to get a collection of arrays like z.find_by_hash({'a' => 1}) for it to return 

[{'a' => 1, 'b' => 2}, {'a' => 1, 'b => 4}]

Thanks

Upvotes: 1

Views: 843

Answers (4)

Sammy S.
Sammy S.

Reputation: 1290

You can do this:

class Array
  def find_by_hash(hash)
    self.select { |h| h.includes_hash?(hash) }
  end
end

class Hash
  def includes_hash?(other)
    included = true

    other.each do |key, value|
      included &= self[key] == other[key]
    end

    included
  end
end

This extends Hash by a method to find out if a Hash includes another (with multiple keys and values). Array is extended with the method you wanted, but it's a more generic approach since you can do this:

ary = [ {:a => 1, :b => 3, :c => 5}, {:a => 5, :b => 2, :c => 8} ]
ary.find_by_hash( { :a => 1, :c => 5 } )

Note: You should also consider using Symbols for Hash keys since it is a common practice in Ruby, but my approach does also work with your keys.

Upvotes: 1

Siwei
Siwei

Reputation: 21559

I didn't find an approach in API, so I think we have to implement it of our own.
(by the way, I think @megas' approach is better and more readable)

Code by TDD: 

class SearchHashTest < Test::Unit::TestCase
  def setup
    @array_with_hash_elements = ArrayWithHashElements.new [{'a' => 1, 'b' => 2}, {'a' => 3, 'b' => 4}, {'a' => 1, 'b' => 4}]
  end
  def test_search_an_array_by_hash_parameter_and_return_single_hash
    assert_equal( {'a' => 3, 'b' => 4}, @array_with_hash_elements.search({'a'=>3}) )
  end
  def test_search_an_array_by_hash_parameter_and_return_an_array
    assert_equal( [{'a' => 1, 'b' => 2}, {'a'=> 1, 'b' => 4}], @array_with_hash_elements.search({'a'=>1}))
  end
end

implemented code ( just for demo, not production) 

class ArrayWithHashElements
  def initialize some_array
    @elements = some_array
  end
  def search( query_hash)
    puts "search:  #{query_hash.inspect}"
    result = []
    @elements.each do | array_element_in_hash_form|
      query_hash.each_pair do | key, value |
        if array_element_in_hash_form.has_key?(key) && array_element_in_hash_form[key] == value
          puts "adding : #{array_element_in_hash_form.inspect} to result"
          result << array_element_in_hash_form
        end
      end
      result
    end
    return result.size != 1 ? result : result[0]
  end
end

result: 

sg552@siwei-moto:~/workspace/test$ ruby search_hash_test.rb
Loaded suite search_hash_test
Started
search:  {"a"=>1}
adding : {"b"=>2, "a"=>1} to result
adding : {"b"=>4, "a"=>1} to result
.search:  {"a"=>3}
adding : {"b"=>4, "a"=>3} to result
.
Finished in 0.000513 seconds.

2 tests, 2 assertions, 0 failures, 0 errors

Upvotes: 0

Hugo
Hugo

Reputation: 12914

Basically what you need is something like this:

class Array
  def find_by_hash(h)
    h.collect_concat  do |key, value| 
      self.select{|h| h[key] == value}
    end
  end 
end

Upvotes: 0

megas
megas

Reputation: 21791

z = [{'a' => 1, 'b' => 2}, {'a' => 3, 'b' => 4}, {'a' => 1, 'b' => 4}]

class Array
  def search_hash(hash)
    key = hash.keys.first
    value = hash.values.first
    select { |h| h[key] == value }
  end
end

z.search_hash({'a' => 3}) #=> [{"a"=>3, "b"=>4}]

or you can type it without curly brackets

z.search_hash('a' => 3)

Upvotes: 0

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