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例如，我有4个帐单记录。栏目列表记录属性如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"
我想获得像散城市的统计{"Newyork" => 2 , "Boston" => 2 }