Ruby array of hash. group_by and modify in one line

Question

I have an array of hashes, something like

[ {:type=>"Meat", :name=>"one"}, 
  {:type=>"Meat", :name=>"two"}, 
  {:type=>"Fruit", :name=>"four"} ]

and I want to convert it to this

{ "Meat" => ["one", "two"], "Fruit" => ["Four"]}

I tried group_by but then i got this

{ "Meat" => [{:type=>"Meat", :name=>"one"}, {:type=>"Meat", :name=>"two"}],
  "Fruit" => [{:type=>"Fruit", :name=>"four"}] }

and then I can't modify it to leave just the name and not the full hash. I need to do this in one line because is for a grouped_options_for_select on a Rails form.

Solution 1

array.group_by{|h| h[:type]}.each{|_, v| v.replace(v.map{|h| h[:name]})}
# => {"Meat"=>["one", "two"], "Fruit"=>["four"]}

Following steenslag's suggestion:

array.group_by{|h| h[:type]}.each{|_, v| v.map!{|h| h[:name]}}
# => {"Meat"=>["one", "two"], "Fruit"=>["four"]}

Solution 2

In a single iteration over initial array:

arry.inject(Hash.new([])) { |h, a| h[a[:type]] += [a[:name]]; h }

Solution 3

Using ActiveSuport's Hash#transform_values:

array.group_by{ |h| h[:type] }.transform_values{ |hs| hs.map{ |h| h[:name] } }
#=> {"Meat"=>["one", "two"], "Fruit"=>["four"]}

Solution 4

array = [{:type=>"Meat", :name=>"one"}, {:type=>"Meat", :name=>"two"}, {:type=>"Fruit", :name=>"four"}]
array.inject({}) {|memo, value| (memo[value[:type]] ||= []) << value[:name]; memo}

Solution 5

I would do as below :

hsh =[{:type=>"Meat", :name=>"one"}, {:type=>"Meat", :name=>"two"}, {:type=>"Fruit", :name=>"four"}]
p Hash[hsh.group_by{|h| h[:type] }.map{|k,v| [k,v.map{|h|h[:name]}]}]

# >> {"Meat"=>["one", "two"], "Fruit"=>["four"]}

View more solutions

Comments

[Stefan]

There's an option_groups_from_collection_for_select helper.

[steenslag]

The last block can be written as {|_, v| v.map!{|h| h[:name]}}

[sawa]

@steenslag Thanks. I forgot about it.

[Cary Swoveland]

...or each_value..., and don't see why the !.

[Cary Swoveland]

Nice! (But your preamble sounds like a drum roll. :-) )

[Cary Swoveland]

.each_value {|v| v.map!{|h| h[:name]}} works, but I see ! is needed.

[Cary Swoveland]

Your answer has given me greater insight into the coolness of inject. Thanks!

[Matstar]

transform_values is now part of Ruby itself (since 2.4, I think).