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例如，我有4個帳單記錄。欄目列表記錄屬性如x
id = 1
prize = 100
city = "newyork"
id = 2
prize = 200
city = "NEWYORK"
id = 3
prize = 300
city = "Boston"
id = 4
prize = 400
city = "BOSTON"
我想獲得像散城市的統計{"Newyork" => 2 , "Boston" => 2 }