How to construct the 2d structure in a dynamic fashion

I iterate through all cars and its supported attributes (many attributes per car) to create a structure like this, how do I do this in a dynamic fashion.

cars = {
   "honda" => {'color' => 'blue', 'type' => 'sedan'}.
   "nissan" => {'color' => 'yellow', 'type' => 'sports'}.
...
}

cars.each do |car|
   car_attrs = ...
   car_attrs.each do |attr|
     ??? How to construct the above structure
 开发者_运维知识库  end
end

Your question is not very clear... But i guess this is what you want:

cars = {}
options = {}
options['color'] = 'blue'
...
cars['honda'] = options

Is that what you were looking for?

It sounds like you may be asking for a way to create a 2-dimensional hash without having to explicitly create each child hash. One way to accomplish that is by specifying the default object created for a hash key.

# When we create the cars hash, we tell it to create a new Hash
# for undefined keys
cars = Hash.new { |hash, key| hash[key] = Hash.new }

# We can then assign values two-levels deep as follows
cars["honda"]["color"] = "blue"
cars["honda"]["type"] = "sedan"
cars["nissan"]["color"] = "yellow"
cars["nissan"]["type"] = "sports"

# But be careful not to check for nil using the [] operator
# because a default hash is now created when using it
puts "Found a Toyota" if cars["toyota"]

# The correct way to check would be
puts "Really found a Toyota" if cars.has_key? "toyota"

Many client libraries assume that the [] operator returns a nil default, so make sure other code doesn't depend on that behavior before using this solution. Good luck!

Assuming you are using something similar to ActiveRecord (but easy to modify if you are not):

cars_info = Hash[cars.map { |car| [car.name, car.attributes] }