Summing up values inside an array of hashes in Ruby

Question

I have the following array of hashes:

books = [
  {'author' => 'John Doe', 'month' => 'June', 'sales' => 500},
  {'author' => 'George Doe', 'month' => 'June', 'sales' => 600},
  {'author' => 'John Doe', 'month' => 'July', 'sales' => 700},
  {'author' => 'George Doe', 'month' => 'July', 'sales' => 800}
]

Out of this, how can I get an array, with the following:

[
  {'author' => 'John Doe', 'total_sales' => 1200},
  {'author' => 'George Doe', 'total_sales' => 1400}
]

Answer 1

您可以使用each_with_object适当的默认值：

default = Hash.new {|h,k| h[k] = { 'author' => k, 'total_sales' => 0 } }
books.each_with_object(default) do |h, memo|
  memo[h['author']]['total_sales'] += h['sales']
end.values

输出：

[
  {"author"=>"John Doe", "total_sales"=>1200}, 
  {"author"=>"George Doe", "total_sales"=>1400}
]