hash group

a.rb

a = [{:id=>1, :phone=>2}, {:id=>1, :phone=>3}, {:id=>2, :phone=>2}]

a.group_by { |item| item[:id] }
{1=>[{:id=>1, :phone=>2}, {:id=>1, :phone=>3}], 2=>[{:id=>2, :phone=>2}]}

b = _[1]
[{:id=>1, :phone=>2}, {:id=>1, :phone=>3}]

b.map { |h| h[:phone] }
[2, 3]

# so combine everything
a.group_by { |h| h[:id] }.map { |id, hs| { id: id, phone: hs.map { |h| h[:phone] }} }