Question

If I have an array of hashes, each with a day key:

[
    {:day=>4,:name=>'Jay'},
    {:day=>1,:name=>'Ben'},
    {:day=>4,:name=>'Jill'}
]

What is the best way to convert it to a hash with sorted day values as the keys:

{
    :1=>[{:day=>1,:name=>'Ben'}],
    :4=>[{:day=>4,:name=>'Jay'},{:day=>4,:name=>'Jill'}]
}

I’m using Ruby 1.9.2 and Rails 3.1.1

Answer 1

Personally, I wouldn’t bother “sorting” the keys (which amounts to ordering-by-entry-time in Ruby 1.9) until I actually needed to. Then you can use group_by:

arr = [{:day=>4,:name=>'Jay'}, {:day=>1,:name=>'Ben'}, {:day=>4,:name=>'Jill'}]
arr.group_by { |a| a[:day] }
=> {4=>[{:day=>4, :name=>"Jay"}, {:day=>4, :name=>"Jill"}],
    1=>[{:day=>1, :name=>"Ben"}]}

Instead, sort the keys when you actually need them.