[英]How to get a distinct list from a List of objects?
I have a List<MyClass> someList
.我有一个
List<MyClass> someList
。
class MyClass
{
public int Prop1...
public int Prop2...
public int Prop3...
}
I would like to know how to get a new distinct List<MyClass> distinctList
from List<MyClass> someList
, but only comparing it to Prop2
.我想知道如何从
List<MyClass> someList
获得一个新的不同List<MyClass> distinctList
,但只将它与Prop2
进行比较。
You can emulate the effect of DistinctBy
using GroupBy
and then just using the first entry in each group.您可以使用
GroupBy
模拟DistinctBy
的效果,然后仅使用每个组中的第一个条目。 Might be a bit slower that the other implementations though.虽然可能比其他实现慢一点。
someList.GroupBy(elem=>elem.Prop2).Select(group=>group.First());
Unfortunately there's no really easy built-in support for this in the framework - but you can use the DistinctBy
implementation I have in MoreLINQ .不幸的是,在框架中并没有真正简单的内置支持——但您可以使用我在MoreLINQ中的
DistinctBy
实现。
You'd use:你会使用:
var distinctList = someList.DistinctBy(x => x.Prop2).ToList();
(You can take just the DistinctBy
implementation. If you'd rather use a Microsoft implementation, I believe there's something similar in the System.Interactive assembly of Reactive Extensions .) (您可以只采用
DistinctBy
实现。如果您更愿意使用 Microsoft 实现,我相信Reactive Extensions的 System.Interactive 程序集中有类似的东西。)
you need to use .Distinct(..);
你需要使用
.Distinct(..);
extension method.扩展方法。 Here's a quick sample:
这是一个快速示例:
public class Comparer : IEqualityComparer<Point>
{
public bool Equals(Point x, Point y)
{
return x.X == y.X;
}
public int GetHashCode(Point obj)
{
return (int)obj.X;
}
}
Do not forget about GetHashCode
.不要忘记
GetHashCode
。
Usage:用法:
List<Point> p = new List<Point>();
// add items
p.Distinct(new Comparer());
Override Equals(object obj) and GetHashCode() methods:覆盖Equals(object obj)和GetHashCode()方法:
class MyClass
{
public int Prop1 { get; set; }
public int Prop2 { get; set; }
public int Prop3 { get; set; }
public override bool Equals(object obj)
{
return ((MyClass)obj).Prop2 == Prop2;
}
public override int GetHashCode()
{
return Prop2.GetHashCode();
}
}
and then just call:然后只需调用:
List<MyClass> distinctList = someList.Distinct().ToList();
Since the introduction of value tuples, if you want a LINQ equivalent to SQL's DISTINCT自从引入了值元组,如果你想要一个相当于 SQL 的 DISTINCT 的 LINQ
items.GroupBy(item => (item.prop1, item.prop2, ...)).Select(group => group.First())
If you would like to Distinct
your list by multiple fields, You have to create an instance of IEqualityComparer
interface:如果你想通过多个字段
Distinct
你的列表,你必须创建一个IEqualityComparer
接口的实例:
public class MyComparer : IEqualityComparer<MyModel>
{
public bool Equals(MyModel x, MyModel y)
{
// compare multiple fields
return
x.Field1 == y.Field1 &&
x.Field2 == y.Field2 &&
x.Field3 == y.Field3 ;
}
public int GetHashCode(MyModel obj)
{
return
obj.Field1.GetHashCode() +
obj.Field2.GetHashCode() +
obj.Field3.GetHashCode();
}
}
Then use the comparer to distinct your list:然后使用比较器来区分您的列表:
var distinctedList = myList.Distinct(new MyComparer()).ToList();
Create a class that implements the IEqualityComparer Interface that only checks for your Prop2-Property.创建一个实现IEqualityComparer接口的类,该接口仅检查您的 Prop2-Property。 You can then pass an instance of this class to the Distinct extension method.
然后,您可以将此类的实例传递给 Distinct 扩展方法。
I know it's been a while, but I needed the simplest answer and at this time (with .NET 4.5.1) I found the following to be the most straight-forward answer I could get to:我知道这已经有一段时间了,但我需要最简单的答案,此时(使用 .NET 4.5.1)我发现以下是我能得到的最直接的答案:
IEnumerable<long> allIds = waitingFiles.Values.Select(wf => wf.groupId).Distinct();
My situation is that I have a ConcurrentDictionary that looks something like: ConcurrentDictionary<long, FileModel>
我的情况是我有一个看起来像这样的 ConcurrentDictionary:
ConcurrentDictionary<long, FileModel>
The ConcurrentDictionary Values property is basically my List<FileModel>
. ConcurrentDictionary Values 属性基本上是我的
List<FileModel>
。
*FileModel has a groupId that isn't necessarily unique (though, obviously the key (long) that I use to add the FileModel object into the dictionary is unique to the FileModel). *FileModel 有一个不一定唯一的 groupId(尽管,显然我用来将 FileModel 对象添加到字典中的键(长)对于 FileModel 是唯一的)。
*Named for clarity in the example. *为示例中的清晰起见命名。
The point is that I have a large number of FileModels (imagine 100) in the ConcurrentDictionary and within those 100 FileModels there are 5 different groupIds.关键是我在 ConcurrentDictionary 中有大量的 FileModel(假设有 100 个),在这 100 个 FileModel 中有 5 个不同的 groupId。
At this point I just need a list of the distinct groupId.此时我只需要一个不同 groupId 的列表。
So, again if I just had a list of FileModel the code would look like the following:所以,如果我只有一个 FileModel 列表,代码将如下所示:
IEnumerable <long> allIds = allFileModel.Select(fm => fm.groupId).Distinct();
I have a List<MyClass> someList
.我有一个
List<MyClass> someList
。
class MyClass
{
public int Prop1...
public int Prop2...
public int Prop3...
}
I would like to know how to get a new distinct List<MyClass> distinctList
from List<MyClass> someList
, but only comparing it to Prop2
.我想知道如何从
List<MyClass> someList
获得一个新的不同List<MyClass> distinctList
,但只将它与Prop2
进行比较。
Simple way to remove duplications where all properties are equal:删除所有属性都相等的重复项的简单方法:
System.Web.Script.Serialization.JavaScriptSerializer jss = new System.Web.Script.Serialization.JavaScriptSerializer();
serviceList = serviceList.GroupBy(s => jss.Serialize(s)).Select(group => group.First()).ToList();
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