In Rails, what is the best way to compact a hash into a nested hash

Question

Say I have this:

[
  { :user_id => 1, :search_id => a},
  { :user_id => 1, :search_id => b},
  { :user_id => 2, :search_id => c},
  { :user_id => 2, :search_id => d}
]

and I want to end up with:

[
  { :user_id => 1, :search_id => [a,b]},
  { :user_id => 2, :search_id => [c,d]}
]

What is the best way to do that?

Answer 1

Very strange requirement indeed. Anyway

[ { :user_id => 1, :search_id => "a"},
  { :user_id => 1, :search_id => "b"},
  { :user_id => 2, :search_id => "c"},
  { :user_id => 2, :search_id => "d"} ] \
    .map{ |h| h.values_at(:user_id, :search_id) } \
    .group_by(&:first) \
    .map{ |k, v| { :user_id => k, :search_id => v.map(&:last) } }