Ruby-如何将数组添加到哈希键？

Question

I have this loop:

car_data = Hash.new
Car.all.each do |c|
  car_data[c.brand] = c.id
  car_data['NEW'] << c.id if c.new == 1
end

I have this snipper and trying to save all the new cars to car_data['NEW'] , but this code keeps only one item in the hash (there should be 8).

I also tried to define that car_data['NEW'] as an array:

car_data = Hash.new
car_data['NEW'] = Hash.new
Car.all.each do |c|
  car_data[c.brand] = c.id
  car_data['NEW'] << c.id if c.new == 1
end

But the result was the same - just one item. How do I save the whole array to the hash key element?

Thank you.

Answer 1

You wrote, that you tried to define (initialize) car_data['NEW'] as an array, but what you did is... initialized it as a hash.

Change:

car_data['NEW'] = Hash.new

To:

car_data['NEW'] = []

The full code would look like:

car_data = Hash.new
car_data['NEW'] = []
Car.all.each do |c|
  car_data[c.brand] = c.id
  car_data['NEW'] << c.id if c.new == 1
end

Answer 2

car_data['NEW'] has to be declared as Array .

car_data = Hash.new
car_data['NEW'] = []
Car.all.each do |c|
  car_data[c.brand] = c.id
  car_data['NEW'] << c.id if c.new == 1
end

You can also do it in a single step

car_data = { new: [] }
Car.all.each do |c|
  car_data[c.brand] = c.id
  car_data[:new] << c.id if c.new == 1
end

Frankly, it seems a little bit odd to me to use a Hash in that way. In particular, mixin different kind of information in Hash is a very bad approach inherited from other non object oriented languages.

I'd use at least two separate variables. But I don't know enough about the context to provide a meaningful example.

Answer 3

car_data = Car.all.each_with_object(Hash.new { |h, k| h[k] = [] }) do |c, memo|
  memo[c.brand] = c.id
  memo['NEW'] << c.id if c.new == 1
end

or, simpler, let's create it on the fly if needed:

car_data = Car.all.each_with_object({}) do |c, memo|
  memo[c.brand] = c.id
  (memo['NEW'] ||= []) << c.id if c.new == 1
end

Please also refer to comment by @tadman below, if the NEW key is to be existing in any case.