如何使用帶有min的Linq進行GroupBy？-有解無憂

我必須從串列中顯示按 GoodsCode 分組的電影，然后在每個商品上獲取 ChangeDate 的最大值。

TABLE - GOODS_TABLE
GOODS_CODE GOODS_PRICE CHANGE_DATE GOODS_PART
8800       1000        20220911    1
8800       1200        20220914    1
8801       1300        20220928    2
8801       1500        20220929    2
8802       1300        20220916    3
8802       1500        20221001    3
8802       2400        20221004    3

例如，在這種情況下，我想從 GOODS_TABLE 中獲取它，比如

GOODS_CODE GOODS_PRICE CHANGE_DATE GOODS_PART
8800       1200        20220914    1
8801       1500        20220929    2
8802       2400        20221004    3

在這種情況下，

from p in goods
group p by { p.goods_code, p.goods_price, p.change_date, p.goods_part } into g
select (goods_code: g.Key.goods_code, goods_price: g.Key.goods_price, goods_part : g.Key.goods_part, change_date: g.Max(p => p.change_date));

我想知道我是否應該像上面那樣把我想帶的所有專欄都帶上。

Linq還有其他方法嗎？

uj5u.com熱心網友回復：

嘗試這個

var result = goods.GroupBy(x => x.goods_code).Select(x => x.MaxBy(y => y.change_date));

例子：


class Goods
{
    public int GoodsCode { get; set; }

    public int GoodsPrice { get; set; }

    public int ChangeDate { get; set; }

    public int GoodsPart { get; set; }

    public Goods(int goodsCode, int goodsPrice, int changeDate, int goodsPart)
    {
        GoodsCode = goodsCode;
        GoodsPrice = goodsPrice;
        ChangeDate = changeDate;
        GoodsPart = goodsPart;
    }
}

var goods = new List<Goods>
{
    new Goods(8800, 1000, 20220911, 1),
    new Goods(8800, 1200,  20220914, 1),
    new Goods(8801, 1300, 20220928, 2),
    new Goods(8801, 1500, 20220929, 2),
    new Goods(8802, 1300, 20220916, 3),
    new Goods(8802, 1500, 20221001, 3),
    new Goods(8802, 2400, 20221004, 3)
};

var eachMax = goods.GroupBy(x => x.GoodsCode).Select(x => x.MaxBy(y => y.ChangeDate));
eachMax.ToList().ForEach(x => 
    Console.WriteLine($"{x.GoodsCode} {x.GoodsPrice} {x.ChangeDate} {x.GoodsPart}"));

// 8800 1200 20220914 1
// 8801 1500 20220929 2
// 8802 2400 20221004 3

uj5u.com熱心網友回復：

嘗試這個

var result = goods.GroupBy(g => g.goods_code)
                  .SelectMany(s => s.OrderByDescending(d => d.change_date)
                                    .Take(1));

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