Build hash from collection of ActiveRecord Models

I'm trying to build a hash from a Model.

This is the type of hash I want to build.

{"United Sates" => "us", "United Kingdom" => "uk" .....}

I have tried so many ways now I'm just going around in circles.

Here 开发者_开发技巧are just some of my poor attempts.

select = Array.new
countries.each do |country|
  # select.push({country.name => country.code })
  # select[country.name][country.code]
end

h = {}

countries.each do |c|
  # h[] = {c.name => c.code}
  # h[] ||= {} 
  # h[][:name] = c.name
  # h[][:code] = c.code 
  #h[r.grouping_id][:name] = r.name
  # h[r.grouping_id][:description] = r.description
end

Please can some advise.

Thank You

---

Here are some one-liner alternatives:

# Ruby 2.1+
name_to_code = countries.map{ |c| [c.name,c.code] }.to_h

# Ruby 1.8.7+
name_to_code = Hash[ countries.map{ |c| [c.name,c.code] } ]

# Ruby 1.8.6+
name_to_code = Hash[ *countries.map{ |c| [c.name,c.code] }.flatten ]

# Ruby 1.9+
name_to_code = {}.tap{ |h| countries.each{ |c| h[c.name] = c.code } }

# Ruby 1.9+
name_to_code = countries.to_a.each_with_object({}){ |c,h| h[c.name] = c.code }

Courtesy of @Addicted's comment below:

# Ruby 1.8+
name_to_code = countries.inject({}){ |r,c| r.merge c.name=>c.code }

---

With Rails 4 you could simply do:

country_codes = Hash[Country.pluck(:name, :code)]

Which I think is optimal because you don't have to load a bunch of country objects and iterate through them

The pluck method on Rails 3 does not allow more than one attribute, but you could do something like:

 country_codes = Hash[Country.connection.select_rows(Country.select('name, code').to_sql)]

---

My favorite Answer these days is to use pluck and to_h

countries.pluck(:name, :code).to_h
# => {"United Sates" => "us", "United Kingdom" => "uk" .....}

to reverse them and have the code first

countries.pluck(:code, :name).to_h
# => {"us" => "United Sates", "uk" => "United Kingdom" .....}

---

Define the countries hash then fill it from your records.

countries_hash = {}
countries.each do |c|
  countries_hash[c.name] = c.code
end