Slice a hash to include only the given keys. This is useful for limiting an options hash to valid keys before passing to a method: 

  def search(criteria = {})
    assert_valid_keys(:mass, :velocity, :time)
  end

  search(options.slice(:mass, :velocity, :time))

If you have an array of keys you want to limit to, you should splat them: 

  valid_keys = [:mass, :velocity, :time]
  search(options.slice(*valid_keys))
Methods
Public Instance methods
slice(*keys)

Returns a new hash with only the given keys.

[ show source ]

    # File activesupport/lib/active_support/core_ext/hash/slice.rb, line 19
19:         def slice(*keys)
20:           keys = keys.map! { |key| convert_key(key) } if respond_to?(:convert_key)
21:           hash = self.class.new
22:           keys.each { |k| hash[k] = self[k] if has_key?(k) }
23:           hash
24:         end
slice!(*keys)

Replaces the hash with only the given keys. Returns a hash contained the removed key/value pairs 

  {:a => 1, :b => 2, :c => 3, :d => 4}.slice!(:a, :b) # => {:c => 3, :d =>4}

[ show source ]

    # File activesupport/lib/active_support/core_ext/hash/slice.rb, line 29
29:         def slice!(*keys)
30:           keys = keys.map! { |key| convert_key(key) } if respond_to?(:convert_key)
31:           omit = slice(*self.keys - keys)
32:           hash = slice(*keys)
33:           replace(hash)
34:           omit
35:         end