var data = new List<Product> { 
   new Product{Maker="耐克", Name="篮球鞋", Location="上海"},
   new Product{Maker="耐克", Name="篮球鞋", Location="北京"},
   new Product{Maker="耐克", Name="足球鞋", Location="上海"},
   new Product{Maker="阿迪达斯", Name="篮球鞋", Location="上海"},
};

var result = (from p in data
              group p by new { p.Maker, p.Location } into g
              select new Product { 
                 Maker = g.Key.Maker,
                 Location = g.Key.Location,
                 Name = string.Join("+", g.Select(p => p.Name).ToArray())
              }).ToList();