Group and sum array of hashes by date

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I have an array of hashes like this:

[{:created=>Fri, 22 Jan 2014 13:02:13 UTC +00:00, :amount=>20}, {:created=>Fri, 27 Jan 2014 13:14:57 UTC +00:00, :amount=>15}, {:created=>Fri, 27 Jan 2014 14:42:40 UTC +00:00, :amount=>10}, {:created=>Fri, 28 Jan 2014 15:26:58 UTC +00:00, :amount=>10}, {:created=>Fri, 28 Jan 2014 15:30:18 UTC +00:00, :amount=>20}, {:created=>Fri, 31 Jan 2014 15:32:46 UTC +00:00, :amount=>50}, {:created=>Fri, 31 Jan 2014 15:33:29 UTC +00:00, :amount=>40}]

I'd like to group those hashes by date and sum the amounts. So, in my example, the output would be:

[{:created=>"2014-01-22", :amount=>20}, {:created=>"2014-01-27", :amount=>25}, {:created=>"2014-01-28", :amount=>30}, {:created=>"2014-01-31", :amount=>90}]require 'date'a = [{:created=> 'Fri, 22 Jan 2014 13:02:13 UTC +00:00', :amount=>20}, {:created=>'Fri, 27 Jan 2014 13:14:57 UTC +00:00', :amount=>15}, {:created=>'Fri, 27 Jan 2014 14:42:40 UTC +00:00', :amount=>10}, {:created=>'Fri, 28 Jan 2014 15:26:58 UTC +00:00', :amount=>10}, {:created=>'Fri, 28 Jan 2014 15:30:18 UTC +00:00', :amount=>20}, {:created=>'Fri, 31 Jan 2014 15:32:46 UTC +00:00', :amount=>50}, {:created=>'Fri, 31 Jan 2014 15:33:29 UTC +00:00', :amount=>40}]
 a.group_by { |h| Date.parse h[:created] }.map { |k,v|{:created => k.to_s,:amount => v.map {|h1| h1[:amount]}.inject(:+)}}

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