C# LINQ 获取不同的值并填充 LIST
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LINQ Get Distinct values and fill LIST
提问by scarpacci
I am trying to figure out if I can use LINQ to provide me with the distinct values of some data I have in a DataTable (FirstName, LastName, QTY). I can get the distinct values and fill my List, but I have to run two different LINQ queries to get it....I am sure there is a better way to do it :)
我想弄清楚是否可以使用 LINQ 为我提供 DataTable 中某些数据的不同值（名字、姓氏、数量）。我可以获取不同的值并填充我的列表，但我必须运行两个不同的 LINQ 查询才能获取它......我相信有更好的方法来做到这一点:)
Any suggestions would be greatly appreciated (very new to LINQ)
任何建议将不胜感激（对 LINQ 非常新）
Code:
代码：
public static List<StudentData> LinqDistinct(DataTable dt)
{
DataTable linqTable = dt;
//get the distinct values
var query =
(from names in dt.AsEnumerable()
select new {
FirstName = names.Field<string>("FirstName"),
LastName = names.Field<string>("LastName")
}).Distinct();
//fill my list with the distinct values
List<StudentData> sList = (from sa in query.AsEnumerable()
select new StudentData
{
FirstName = sa.FirstName,
LastName = sa.LastName
//Qty = names.Field<int>("Qty")
}).ToList();
return sList;}
采纳答案by ShuggyCoUk
Any reason not to simply do the projection after the distinct, you might need an AsEnumerable() after the Distinct but that's not a big deal.
任何不简单地在 distinct 之后进行投影的理由，您可能需要在 Distinct 之后使用 AsEnumerable() ，但这没什么大不了的。
public static List<StudentData> LinqDistinct(DataTable dt)
{
DataTable linqTable = dt;
return
(from names in dt.AsEnumerable()
select new {
FirstName = names.Field<string>("FirstName"),
LastName = names.Field<string>("LastName")
}).Distinct().Select(x =>
new StudentData() { FirstName=x.FirstName, LastName=x.LastName})
.ToList();
}
回答by bytebender
Pretty sure you could just do this...
很确定你可以做到这一点......
List<StudentData> sList = (from names in dt.AsEnumerable().Distinct() // I am not sure if you even have to call AsEnumerable()
select new StudentData() {
FirstName = names.Field<string>("FirstName"),
LastName = names.Field<string>("LastName")
}).ToList();
回答by Ecyrb
You could use GroupBy:
你可以使用GroupBy：
public static List<StudentData> LinqDistinct(DataTable dt)
{
List<StudentData> results = dt.AsEnumerable()
.GroupBy(row =>
{
FirstName = row.Field<string>("FirstName"),
LastName = row.Field<string>("LastName")
})
.Select(group => new StudentData
{
FirstName = group.Key.FirstName,
LastName = group.Key.LastName,
Qty = group.Count()
})
.ToList();
return results;
}
class StudentData
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int Qty { get; set; }
}
回答by Joel Mueller
It's not clear from your question whether the quantity is a value in your DataTable, or a count of the number of duplicates for a given item, as in Ecyrb's answer. However, if your StudentDataclass implements IEquatable<StudentData>or overrides the Equals method, this should work:
从您的问题中不清楚数量是您的 DataTable 中的一个值，还是给定项目的重复数量的计数，如 Ecyrb 的回答。但是，如果您的StudentData类实现IEquatable<StudentData>或覆盖了 Equals 方法，这应该有效：
public static List<StudentData> LinqDistinct(DataTable dt)
{
return dt.AsEnumerable()
.Select(row => new StudentData
{
FirstName = row.Field<string>("FirstName"),
LastName = row.Field<string>("LastName"),
Qty = row.Field<int>("Qty")
})
.Distinct()
.ToList();
}
If StudentDatadoesn't support value comparison, and you can't add that support to the class, you may have to create an implementation of IEqualityComparer<StudentData>and pass that into the Distinctmethod.
如果StudentData不支持值比较，并且您无法向类添加该支持，则可能必须创建 的实现IEqualityComparer<StudentData>并将其传递到Distinct方法中。
