如何使用Linq选择最接近指定日期的记录?这适用于具有日期,产品ID,位置ID和余额的交易表。
鉴于这些要求:
表格数据:
// code
Id, TransDateTime, ProductId, WarehouseId, Balance
1, 1-Jan-2011 00:00, 1, 1, 100
2, 1-Jan-2011 00:00, 1, 2, 10
3, 2-Jan-2011 00:00, 1, 1, 150
4, 3-Jan-2011 00:00, 1, 2, 25
5, 3-Jan-2011 00:00, 2, 1, 333
6, 7-Jan-2011 00:00, 1, 1, 149
7, 7-Jan-2011 01:00, 1, 2, 30
8, 7-Jan-2011 02:00, 1, 2, 35
测试日期和输出
Date: 1-Jan would output:
1, 1-Jan-2011 00:00, 1, 1, 100
2, 1-Jan-2011 00:00, 1, 2, 10
Date: 3-Jan would output:
3, 2-Jan-2011 00:00, 1, 1, 150
4, 3-Jan-2011 00:00, 1, 2, 25
5, 3-Jan-2011 00:00, 2, 1, 333
// product 1, warehouse 1 wasn't sold on the 3rd
// so the row from 2-Jan is returned
Date: 7-Jan would output:
5, 3-Jan-2011 00:00, 2, 1, 333
6, 7-Jan-2011 00:00, 1, 1, 149
9, 7-Jan-2011 02:00, 1, 2, 35
// product 2, warehouse 1 wasn't sold on the 7th
// so the row from 3-Jan is returned
// product 1, warehouse 2 was sold twice on the 7th
// so the later one is used
我认为这需要分组(产品 - >仓库 - >日期)或类似的。它超出了我的linq能力!
答案 0 :(得分:5)
步骤:
1)过滤掉inputDate
之后发生的交易
2)按产品和仓库分组剩余交易
3)在每组中找到最近的交易
4)格式化结果对象
直接实施:
DateTime inputDate = ...;
var result = transactions
.Where(t => t.TransDateTime.Date <= inputDate.Date)
.GroupBy(t => new {t.ProductId, t.WarehouseId})
.Select(x => new {
x.Key,
LastTransaction = x.OrderByDescending(t => t.TransDateTime).First(),
})
.Select(x => new {
Id = x.LastTransaction.Id,
Date = x.LastTransaction.TransDateTime,
ProductId = x.Key.ProductId,
WarehouseId = x.Key.WarehouseId,
Balance = x.LastTransaction.Balance,
});
如果您需要进行一些优化,可以考虑为MaxBy
实施IEnumerable
扩展方法,以替换x.OrderByDescending(t => t.TransDateTime).First()
。如果您有许多交易,它会提高效果,因为它是O(n)
而不是O(n log n)
。 MaxBy
实施可以在此处执行,例如:Simple LINQ question in C#