{
 "firstName": "John",
 "lastName": "Smith",
 "age": 25,
 "address":
 {
     "streetAddress": "21 2nd Street",
     "city": "New York",
     "state": "NY",
     "postalCode": "10021"
 },
 "phoneNumber":
 [
     {
       "type": "home",
       "number": "212 555-1234"
     },
     {
       "type": "fax",
       "number": "646 555-4567"
     }
 ]
}

h.select {|k,v| ["age", "address"].include?(k) }

class Hash
  def select_keys(*args)
    select {|k,v| args.include?(k) }
  end
end

h.select_keys("age", "address")

hash.slice('firstName', 'lastName')
 # => { 'firstName' => 'John', 'lastName' => 'Smith' }

h = { "a" => 100, "b" => 200, "c" => 300 }
   h.select {|k,v| k > "a"}  #=> {"b" => 200, "c" => 300}
   h.select {|k,v| v < 200}  #=> {"a" => 100}

h.select {|k,v| k == "age" || k == "address" }

hash = { a: true, b: false, c: nil}
hash.except!(:c) # => { a: true, b: false}
hash # => { a: true, b: false }

class Hash
  def select_keys(*args)
    filtered_hash = {}
    args.each do |arg|
      filtered_hash[arg] = self[arg] if self.has_key?(arg)
    end
    return filtered_hash
  end
end

keys = [ "firstName" , "address" ]
keys.zip(hash.values_at *keys).to_h