我有一个员工
的集合Class Employee
{
empName
empID
empLoc
empPL
empShift
}
我的列表包含
empName,empID,empLoc,empPL,empShift
E1,1,L1,EPL1,S1
E2,2,L2,EPL2,S2
E3,3,L3,EPL3,S3
E4,4,L1,EPL1,S1
E5,5,L5,EPL5,S5
E6,6,L2,EPL2,S2
我需要让员工拥有不同的价值观 empLoc,empPL,empShift。
有没有办法用LINQ实现这个目的?
答案 0 :(得分:38)
您可以实施自定义IEqualityComparer<Employee>
:
public class Employee
{
public string empName { get; set; }
public string empID { get; set; }
public string empLoc { get; set; }
public string empPL { get; set; }
public string empShift { get; set; }
public class Comparer : IEqualityComparer<Employee>
{
public bool Equals(Employee x, Employee y)
{
return x.empLoc == y.empLoc
&& x.empPL == y.empPL
&& x.empShift == y.empShift;
}
public int GetHashCode(Employee obj)
{
unchecked // overflow is fine
{
int hash = 17;
hash = hash * 23 + (obj.empLoc ?? "").GetHashCode();
hash = hash * 23 + (obj.empPL ?? "").GetHashCode();
hash = hash * 23 + (obj.empShift ?? "").GetHashCode();
return hash;
}
}
}
}
现在您可以使用Enumerable.Distinct
的重载:
var distinct = employees.Distinct(new Employee.Comparer());
使用匿名类型的可重用性较低,功能强大且效率较低的方法:
var distinctKeys = employees.Select(e => new { e.empLoc, e.empPL, e.empShift })
.Distinct();
var joined = from e in employees
join d in distinctKeys
on new { e.empLoc, e.empPL, e.empShift } equals d
select e;
// if you want to replace the original collection
employees = joined.ToList();
答案 1 :(得分:35)
您可以将GroupBy
与匿名类型一起使用,然后获取First
:
list.GroupBy(e => new {
empLoc = e.empLoc,
empPL = e.empPL,
empShift = e.empShift
})
.Select(g => g.First());
答案 2 :(得分:11)
您可以尝试使用此代码
var result = (from item in List
select new
{
EmpLoc = item.empLoc,
EmpPL= item.empPL,
EmpShift= item.empShift
})
.ToList()
.Distinct();
答案 3 :(得分:3)
我很想知道哪种方法会更快:
我发现根据输入数据的大小和组的数量,Distinct方法可以提高性能。 (因为组的数量倾向于列表中的元素数量,不同的运行速度更快)。
代码在LinqPad中运行!
void Main()
{
List<C> cs = new List<C>();
foreach(var i in Enumerable.Range(0,Int16.MaxValue*1000))
{
int modValue = Int16.MaxValue; //vary this value to see how the size of groups changes performance characteristics. Try 1, 5, 10, and very large numbers
int j = i%modValue;
cs.Add(new C{I = i, J = j});
}
cs.Count ().Dump("Size of input array");
TestGrouping(cs);
TestDistinct(cs);
}
public void TestGrouping(List<C> cs)
{
Stopwatch sw = Stopwatch.StartNew();
sw.Restart();
var groupedCount = cs.GroupBy (o => o.J).Select(s => s.First()).Count();
groupedCount.Dump("num groups");
sw.ElapsedMilliseconds.Dump("elapsed time for using grouping");
}
public void TestDistinct(List<C> cs)
{
Stopwatch sw = Stopwatch.StartNew();
var distinctCount = cs.Distinct(new CComparerOnJ()).Count ();
distinctCount.Dump("num distinct");
sw.ElapsedMilliseconds.Dump("elapsed time for using distinct");
}
public class C
{
public int I {get; set;}
public int J {get; set;}
}
public class CComparerOnJ : IEqualityComparer<C>
{
public bool Equals(C x, C y)
{
return x.J.Equals(y.J);
}
public int GetHashCode(C obj)
{
return obj.J.GetHashCode();
}
}
答案 4 :(得分:0)
尝试,
var newList =
(
from x in empCollection
select new {Loc = x.empLoc, PL = x.empPL, Shift = x.empShift}
).Distinct();