Search an Array of Hashes with a partial Hash in Ruby - ruby

Question

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

Answer 1

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.

Answer 2

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)

Answer 3

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

Answer 4

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