How to group an array of hashes by key?

Question

ruby

There is an array consisting of hashes:

[
  {:car=>["BMW", "Mersedes", "Audi"]},
  {:car=>["Renault", "Ferrari", "Nissan"]},
  {:car=>["VW"]},
  {:country=>["Russia", "Japan", "USA"]},
  {:country=>["China", "Nigeria", "Egypt"]},
  {:city=>["Moscow", "Tokyo", "Amsterdam"]}
]

You need to group hashes by key, like:

[
  {:car=>},
  {:country=>},
  {:city=>["Moscow", "Tokyo", "Amsterdam"]}
]

those. concatenate arrays with the same key.

Answer 1

a = [
  {:car=>["BMW", "Mersedes", "Audi"]},
  {:car=>["Renault", "Ferrari", "Nissan"]},
  {:car=>["VW"]},
  {:country=>["Russia", "Japan", "USA"]},
  {:country=>["China", "Nigeria", "Egypt"]},
  {:city=>["Moscow", "Tokyo", "Amsterdam"]}
]

b = a.group_by{|n| n.keys[0]}.map{|k, n| {k => n.map{|m| m[k]}}}