iequalitycomparer

Pass a lambda expression in place of IComparer or IEqualityComparer or any single-method interface?

由 不想你离开。 提交于 2019-11-27 11:52:48
问题 I happened to have seen some code where this guy passed a lambda expression to a ArrayList.Sort(IComparer here) or a IEnumerable.SequenceEqual(IEnumerable list, IEqualityComparer here) where an IComparer or an IEqualityComparer was expected. I can't be sure if I saw it though, or I am just dreaming. And I can't seem to find an extension on any of these collections that accepts a Func<> or a delegate in their method signatures. Is there such an overload/extension method? Or, if not, is it

Using IEqualityComparer GetHashCode with a tolerance

由 ＊爱你＆永不变心＊ 提交于 2019-11-27 07:10:00
问题 I am trying to implement an IEqualityComparer that has a tolerance on a date comparison. I have also looked into this question. The problem is that I can't use a workaround because I am using the IEqualityComparer in a LINQ .GroupJoin() . I have tried a few implementations that allow for tolerance. I can get the Equals() to work because I have both objects but I can't figure out how to implement GetHashCode() . My best attempt looks something like this: public class ThingWithDateComparer :

What's the role of GetHashCode in the IEqualityComparer<T> in .NET?

由 岁酱吖の 提交于 2019-11-27 02:54:53
I'm trying to understand the role of the GetHashCode method of the interface IEqualityComparer. The following example is taken from MSDN: using System; using System.Collections.Generic; class Example { static void Main() { try { BoxEqualityComparer boxEqC = new BoxEqualityComparer(); Dictionary<Box, String> boxes = new Dictionary<Box, string>(boxEqC); Box redBox = new Box(4, 3, 4); Box blueBox = new Box(4, 3, 4); boxes.Add(redBox, "red"); boxes.Add(blueBox, "blue"); Console.WriteLine(redBox.GetHashCode()); Console.WriteLine(blueBox.GetHashCode()); } catch (ArgumentException argEx) { Console

IEqualityComparer<T> that uses ReferenceEquals

由 醉酒当歌 提交于 2019-11-27 01:23:14
Is there a default IEqualityComparer<T> implementation that uses ReferenceEquals ? EqualityComparer<T>.Default uses ObjectComparer, which uses object.Equals() . In my case, the objects already implement IEquatable<T> , which I need to ignore and compare by object's reference only. Yurik Just in case there is no default implementation, this is my own: Edit by 280Z28: Rationale for using RuntimeHelpers.GetHashCode(object) , which many of you probably haven't seen before. :) This method has two effects that make it the correct call for this implementation: It returns 0 when the object is null.

List.Contains is not working as hoped

由 我们两清 提交于 2019-11-26 23:17:31
问题 If I have an object of type MyBull and a List<MyBull> orig : // Just an example MyBull x = getMeTheObjectWithIdFromDB(9); orig.add(x); // Again same? data object MyBull y = getMeTheObjectWithIdFromDB(9); Why is this false then? // This is false, even though all the properties // of x and y are the same. orig.Contains<MyBull>(y); 回答1: By default objects will expose reference based equality. If you want custom rules, such as equality based on id fields, you need to override the Equals and

IEqualityComparer for SequenceEqual

由 一世执手 提交于 2019-11-26 22:40:26
In C#, is there a IEqualityComparer<IEnumerable> that uses the SequenceEqual method to determine equality? Cédric Bignon There is no such comparer in .NET Framework, but you can create one: public class IEnumerableComparer<T> : IEqualityComparer<IEnumerable<T>> { public bool Equals(IEnumerable<T> x, IEnumerable<T> y) { return Object.ReferenceEquals(x, y) || (x != null && y != null && x.SequenceEqual(y)); } public int GetHashCode(IEnumerable<T> obj) { // Will not throw an OverflowException unchecked { return obj.Where(e => e != null).Select(e => e.GetHashCode()).Aggregate(17, (a, b) => 23 * a +

How to use the IEqualityComparer

由 我的未来我决定 提交于 2019-11-26 20:14:42
I have some bells in my database with the same number. I want to get all of them without duplication. Then I create a compare class to do this work, but the execution of the function makes a big delay from the function without distinct, from 0.6 sec to 3.2 sec! Am I doing it right or I have to use another method? reg.AddRange((from a in this.dataContext.reglements join b in this.dataContext.Clients on a.Id_client equals b.Id where a.date_v <= datefin && a.date_v >= datedeb where a.Id_client == b.Id orderby a.date_v descending select new Class_reglement { nom = b.Nom, code = b.code, Numf = a

IEqualityComparer for anonymous type

由 有些话、适合烂在心里 提交于 2019-11-26 19:49:37
问题 I have this var n = ItemList.Select(s => new { s.Vchr, s.Id, s.Ctr, s.Vendor, s.Description, s.Invoice }).ToList(); n.AddRange(OtherList.Select(s => new { s.Vchr, s.Id, s.Ctr, s.Vendor, s.Description, s.Invoice }).ToList();); I would like to do this if it where allowed n = n.Distinct((x, y) => x.Vchr == y.Vchr)).ToList(); I tried using the generic LambdaComparer but since im using anonymous types there is no type associate it with. "Help me Obi Wan Kenobi, you're my only hope" 回答1: The trick

What is the difference between IEqualityComparer<T> and IEquatable<T>?

由 一个人想着一个人 提交于 2019-11-26 15:15:54
问题 I want to understand the scenarios where IEqualityComparer<T> and IEquatable<T> should be used. The MSDN documentation for both looks very similar. 回答1: IEqualityComparer<T> is an interface for an object that performs the comparison on two objects of the type T . IEquatable<T> is for an object of type T so that it can compare itself to another. 回答2: When deciding whether to use IEquatable<T> or IEqualityComparer<T>, one could ask: Is there a preferred way of testing two instances of T for

writing a custom comparer for linq groupby

由 百般思念 提交于 2019-11-26 14:48:45
问题 Again this sample is a very simplified version of my actual problem involving a custom comparer for linq grouping. What have I done wrong? The code below produces the result below (1.2, 0), (4.1, 0), (4.1, 0), (1.1, 0), however I was expecting the following since 1.1 and 1.2 are < 1.0 apart. (1.2, 0), (1.1, 0), (4.1, 0), (4.1, 0), class Program { static void Main(string[] args) { IEnumerable<Point> points = new List<Point> { new Point(1.1, 0.0) , new Point(4.1, 0.0) , new Point(1.2, 0.0) ,
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