我想检索给定Year,最新生效日期的类的记录列表。
按类别,年份,RangeMin,RangeMax分组
Id Class...Year...EffectiveDate...Value...RangeMin...RangeMax
1. A.......2019....2019/1/1.........850......1.........100
2. A.......2019....2019/1/15........840......1.........100
3. A.......2019....2019/2/1.........550......101.......200
4. B.......2019....2019/1/5.........540......1.........100
5. B.......2020....2019/1/5.........650......1.........100
6. B.......2020....2019/5/1.........670......101.......200
7. B.......2020....2019/5/2.........680......101.......200
因此,如果我要查询A类和2019年的所有记录以返回行列表:2,3
如果我要查询B类和2020年的所有记录以返回行列表:5,7
var recordsInDb = (from record in context.records where record.Year == year & record.Class == class_ select record).ToList();
到目前为止,我已经能够获得给定年级的所有记录的列表。 我知道我可以通过降低生效日期来添加订单。但这仍然会返回所有记录,而不仅仅是生效日期最高的记录。
答案 0 :(得分:0)
尝试以下操作:
DataTable dt = new DataTable();
dt.Columns.Add("Id", typeof(int));
dt.Columns.Add("Class", typeof(string));
dt.Columns.Add("Year", typeof(int));
dt.Columns.Add("EffectiveDate", typeof(DateTime));
dt.Columns.Add("Value", typeof(int));
dt.Columns.Add("RangeMin", typeof(int));
dt.Columns.Add("RangeMax", typeof(int));
dt.Rows.Add(new object[] {1, "A", 2019, DateTime.Parse("2019/1/1"), 850,1, 100});
dt.Rows.Add(new object[] {2, "A", 2019, DateTime.Parse("2019/1/15"), 840,1, 100});
dt.Rows.Add(new object[] {3, "A", 2019, DateTime.Parse("2019/2/1"), 550,101, 200});
dt.Rows.Add(new object[] {4, "B", 2019, DateTime.Parse("2019/1/5"), 540,1, 100});
dt.Rows.Add(new object[] {5, "B", 2020, DateTime.Parse("2019/1/5"), 650,1, 100});
dt.Rows.Add(new object[] {6, "B", 2020, DateTime.Parse("2019/5/1"), 670,101, 200});
dt.Rows.Add(new object[] {7, "B", 2020, DateTime.Parse("2019/5/2"), 680,101, 200});
DataTable results = dt.AsEnumerable()
.OrderByDescending(x => x.Field<int>("Year"))
.ThenByDescending(x => x.Field<DateTime>("EffectiveDate"))
.GroupBy(x => new { cl = x.Field<string>("Class"), month = new DateTime(x.Field<DateTime>("EffectiveDate").Year, x.Field<DateTime>("EffectiveDate").Month, 1) })
.Select(x => x.FirstOrDefault())
.CopyToDataTable();
答案 1 :(得分:0)
您可以按条件分组,然后从每个分组中选择最新的分组。
使用查询语法:
MWE <- c("R text1 47 GDP -2.4 3.4", "Euro area but not UK CPI 3.7 6.4", "Argentina -2.4 3.4", "Euro area 3.7 6.4")
gsub("^(?:.*\\b(GDP|CPI)\\b|.*?([+-]?\\d))", "\\1\\2", MWE, perl=TRUE)
## => [1] "GDP -2.4 3.4" "CPI 3.7 6.4" "-2.4 3.4" "3.7 6.4"
我认为使用Fluent / lambda语法会更容易一些,因为var recordsInDb = (from record in context.records
where record.Year == year & record.Class == class_
group record by new { record.Year, record.Class, record.RangeMin, record.RangeMax } into rg
select (
from record in rg
orderby record.EffectiveDate
select record
).Last()
)
.ToList();
仍然需要它:
Last