vb.net 数据表上的 GroupBy 和 Sum
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/17270081/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
GroupBy and Sum on a DataTable
提问by Ramesh Durai
I am using LINQ in VB on a datatable to filter my results.
我在 VB 中的数据表上使用 LINQ 来过滤我的结果。
m_oDataTable.Columns.Add("Name1", GetType(String))
m_oDataTable.Columns.Add("Name2", GetType(String))
m_oDataTable.Columns.Add("Time", GetType(Double))
I am trying to filter the datatable by Name1or Name2based on user selection.
我正在尝试通过Name1或Name2基于用户选择过滤数据表。
groupBy = "Name1"
'groupBy = "Name2"
I grouped my data but I was unable to Sumthe desired field.
我对数据进行了分组，但无法找到Sum所需的字段。
Dim test = From tab In m_oDataTable.AsEnumerable()
Group tab By groupDt = tab.Field(Of String)(groupBy) Into Group
Select Group
'Getting Error
Dim test2 = From tab In m_oDataTable.AsEnumerable()
Group tab By groupDt = tab.Field(Of String)(groupBy) Into Group
Select New With
{
.Grp = Key, ' Error in this line(Key is a type, cannot be used as a expression)
.Sum = Group.Sum(Function(r) Double.Parse(r.Item("Time").ToString()))
}
I tried in c# and got the desired result. But have no luck with VB :(
我在 c# 中尝试过并得到了想要的结果。但是 VB 没有运气:(
var test = from tab in m_oDataTable.AsEnumerable()
group tab by tab.Field<string>(groupBy)
into groupDt
select new
{
Group = groupDt.Key,
Sum = groupDt.Sum(r => double.Parse(r["Time"].ToString()))
};
How to achieve this in VB?
如何在VB中实现这一点？
回答by Dave Williams
Not 100% sure why but VB.Net does not support .Key on query expression syntax. You actually define the key variable in the query. You are trying to use a variable "Key" which has not been defined. Instead you need to use they key you defined in the query (groupDt).
不是 100% 确定为什么，但 VB.Net 不支持 .Key 查询表达式语法。您实际上在查询中定义了关键变量。您正在尝试使用尚未定义的变量“Key”。相反，您需要使用它们在查询中定义的键 (groupDt)。
Change one small line and it should work...
更改一小行，它应该可以工作...
Select New With
{
.Grp = groupDt,
.Sum = Group.Sum(Function(r) Double.Parse(r.Item("Time").ToString()))
}
OR you can use fluent syntax:
或者你可以使用流畅的语法：
Dim test2 = Table.AsEnumerable().GroupBy(Function(row) row.Item("Name1")).Select(Function(group) New With {.Grp = group.Key, .Sum = group.Sum(Function(r) Double.Parse(r.Item("Time").ToString()))})
