Develop Reference

HashSet overlaps does not work as expected

Have the object model as shown below with HashSets:
When I try to find the matching set with the below statement does not work.
Could someone please suggest what am I missing here?
Would HashSet.CreateSetComparer solve the problem, if so could you please suggest how to use it?
HashSet Overlaps Statement:
var requirementSets = new HashSet<RequirementSet>();
// requirementSets has some data.
RequirementSet matchingSet = requirementSets.FirstOrDefault(e => e.RequirementOption s.Overlaps(lineItemRequirementSet.RequirementOptions));
Object Model:
public class RequirementSet : IEquatable<RequirementSet>
{
public ISet<RequirementOption> RequirementOptions { get; } = new HashSet<RequirementOption>();
public bool Equals(RequirementSet other)
{
if (ReferenceEquals(null, other))
{
return false;
}
if (ReferenceEquals(this, other))
{
return true;
}
return Equals(RequirementOptions, other.RequirementOptions);
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj))
{
return false;
}
if (ReferenceEquals(this, obj))
{
return true;
}
if (obj.GetType() != this.GetType())
{
return false;
}
return Equals((RequirementSet) obj);
}
public override int GetHashCode()
{
return RequirementOptions != null ? RequirementOptions.GetHashCode() : 0;
}
}
public class RequirementOption : IEquatable<RequirementOption>
{
public ISet<Requirement> Requirements { get; } = new HashSet<Requirement>();
public bool Equals(RequirementOption other)
{
if (ReferenceEquals(null, other))
{
return false;
}
if (ReferenceEquals(this, other))
{
return true;
}
return Equals(Requirements, other.Requirements);
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj))
{
return false;
}
if (ReferenceEquals(this, obj))
{
return true;
}
if (obj.GetType() != this.GetType())
{
return false;
}
return Equals((RequirementOption) obj);
}
public override int GetHashCode()
{
return Requirements != null ? Requirements.GetHashCode() : 0;
}
}
public class Requirement : IEquatable<Requirement>
{
public string Model {get; set;}
public bool Equals(Requirement other)
{
if (ReferenceEquals(null, other))
{
return false;
}
if (ReferenceEquals(this, other))
{
return true;
}
return ModelName == other.ModelName;
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj))
{
return false;
}
if (ReferenceEquals(this, obj))
{
return true;
}
if (obj.GetType() != this.GetType())
{
return false;
}
return Equals((Requirement) obj);
}
public override int GetHashCode()
{
unchecked
{
var hashCode = ModelName != null ? ModelName.GetHashCode();
return hashCode;
}
}
}

HashSet<T> EqualityComparer that returns equal if SetEquals: which GetHashCode? [duplicate]

I am trying to compare two hashsets of Definition type as EqualityComparer<T>.Default.Equals(value, oldValue). Definition is defined as follows
public class Definition
{
public string Variable { get; set; }
public HashSet<Location> LocationList { get; set; }
public override bool Equals(object obj)
{
Definition other = obj as Definition;
return other.Variable.Equals(this.Variable) && other.LocationList!= null &&this.LocationList != null
&& other.LocationList.Count == this.LocationList.Count
&& other.LocationList == this.LocationList;
}
public override int GetHashCode()
{
return this.Variable.GetHashCode() ^ this.LocationList.Count.GetHashCode();// ^ this.LocationList.GetHashCode();
}
}
public class Location
{
public int Line { get; set; }
public int Column { get; set; }
public int Position { get; set; }
public string CodeTab { get; set; }
public Location(int line, int col, int pos, string tab)
{
Line = line;
Column = col;
Position = pos;
CodeTab = tab;
}
public override bool Equals(object obj)
{
Location other = obj as Location;
return this.CodeTab == other.CodeTab
&& this.Position == other.Position
&& this.Column == other.Column
&& this.Line == other.Line;
}
public override int GetHashCode()
{
return this.CodeTab.GetHashCode() ^ this.Position.GetHashCode()
^ this.Column.GetHashCode() ^ this.Line.GetHashCode();
}
}
Somehow for a similar set, the result is returned as false despite all the information remaining the same. The only difference is that the position of some elements are interchanged, but I know that HashSet won't preserve or check the order while comparing. Can any one advise me on what is going wrong here?
PS: I tried uncommenting this.LocationList.GetHashCode() also, but didn't work.

You need to create a comparer for the sets:
var setComparer = HashSet<Location>.CreateSetComparer();
return other.Variable.Equals(this.Variable) && setComparer.Equals(this.LocationList, other.LocationList);

EqualityComparer<T>.Default will look for an object implementing IEquatable<T>. Otherwise, it will defer to an ObjectEqualityComparer, which simply checks for reference equality. This is why you're seeing false when references are compared.
What you actually want to do is explicitly implement IEquatable<Location>. Note you should really make your properties immutable for this to work properly:
public class Location : IEquatable<Location>
{
public Location(int line, int col, int pos, string tab)
{
Line = line;
Column = col;
Position = pos;
CodeTab = tab;
}
public int Line { get; private set; }
public int Column { get; private set; }
public int Position { get; private set; }
public string CodeTab { get; private set; }
public bool Equals(Location other)
{
if (ReferenceEquals(null, other)) return false;
if (ReferenceEquals(this, other)) return true;
return string.Equals(CodeTab, other.CodeTab) && Column == other.Column && Line == other.Line && Position == other.Position;
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj)) return false;
if (ReferenceEquals(this, obj)) return true;
if (obj.GetType() != this.GetType()) return false;
return Equals((Location) obj);
}
public static bool operator ==(Location left, Location right)
{
return Equals(left, right);
}
public static bool operator !=(Location left, Location right)
{
return !Equals(left, right);
}
public override int GetHashCode()
{
unchecked
{
var hashCode = (CodeTab != null ? CodeTab.GetHashCode() : 0);
hashCode = (hashCode*397) ^ Column;
hashCode = (hashCode*397) ^ Line;
hashCode = (hashCode*397) ^ Position;
return hashCode;
}
}
}
Now if you look at the type EqualityComparer created by Default, you'll see GenericEqualityComparer<Location>:
Console.WriteLine(EqualityComparer<Location>.Default.GetType())

EqualityComparer on a nested object

I would like to compare two list of nested objects. If the parent objects Id differ and/or any of the childrens Id or Baz property differs, I want to consider them changed.
I've implemented my own version of Equals and GetHashCode below, but despite using my own equalitycomparer, Except() still yields a result, while I expect the objects to be equal.
var foo1 = new Foo
{
Id = 1,
Bars = new List<Bar>
{
new Bar
{
Id = 1,
Baz = 1.5
},
new Bar
{
Id = 1,
Baz = 1.5
}
}
};
var foo2 = new Foo
{
Id = 1,
Bars = new List<Bar>
{
new Bar
{
Id = 1,
Baz = 1.5
},
new Bar
{
Id = 1,
Baz = 1.5
}
}
};
var diff = new[] { foo1 }.Except(new[] { foo2 });
public class Foo
{
private sealed class IdBarsEqualityComparer : IEqualityComparer<Foo>
{
public bool Equals(Foo x, Foo y)
{
if (ReferenceEquals(x, y)) return true;
if (ReferenceEquals(x, null)) return false;
if (ReferenceEquals(y, null)) return false;
if (x.GetType() != y.GetType()) return false;
return x.Id == y.Id && Equals(x.Bars, y.Bars);
}
public int GetHashCode(Foo obj)
{
unchecked
{
return (obj.Id * 397) ^ (obj.Bars != null ? obj.Bars.GetHashCode() : 0);
}
}
}
public static IEqualityComparer<Foo> IdBarsComparer { get; } = new IdBarsEqualityComparer();
public int Id { get; set; }
public List<Bar> Bars { get; set; }
}
public class Bar
{
protected bool Equals(Bar other)
{
return Id == other.Id && Baz.Equals(other.Baz);
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj)) return false;
if (ReferenceEquals(this, obj)) return true;
if (obj.GetType() != this.GetType()) return false;
return Equals((Bar) obj);
}
public override int GetHashCode()
{
unchecked
{
return (Id * 397) ^ Baz.GetHashCode();
}
}
public int Id { get; set; }
public double Baz { get; set; }
}

There are three things wrong in your code:
You are not passing the equality comparer to Except method, so it's not being used.
Your GetHashCode implementation in Foo is wrong, it returns different results for same objects, so the Equals method is never called.
You are calling equals on two lists: Equals(x.Bars, y.Bars), this checks for reference equality. You can use SequenceEqual instead to compare elements one by one: x.Bars.SequenceEqual(y.Bars)

C# - Stackoverflow exception when adding to HashSet<T>

I have got a class called Team.
class Team
{
public Team(string name)
{
this.Name = name;
this.Wins = 0;
this.Opponents = new HashSet<Team>();
}
public string Name { get; set; }
public int Wins { get; set; }
public HashSet<Team> Opponents { get; set; }
}
I get a Stackoverflow exception whenever i try to add an existing team with a single opponent in another team's HashSet that has zero Opponents guestTeam.Opponents.Add(homeTeam);
Here hometeam has a single opponents in Opponents while guestTeam.Opponents is still empty.
Its a small test app. Stacktrace's framecount shows 3.
Any ideas why would i get such an exception thrown?

I admit, I can't reproduce error. personally I could go into properly implement of
: IEquatable<Team>
And then:
public bool Equals(Team other)
{
if (ReferenceEquals(null, other)) return false;
if (ReferenceEquals(this, other)) return true;
return string.Equals(this.Name, other.Name) && Equals(this.Opponents, other.Opponents);
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj)) return false;
if (ReferenceEquals(this, obj)) return true;
if (obj.GetType() != this.GetType()) return false;
return Equals((Team)obj);
}
public override int GetHashCode()
{
unchecked
{
return ((this.Name != null ? this.Name.GetHashCode() : 0) * 397) ^ (this.Opponents != null ? this.Opponents.GetHashCode() : 0);
}
}
public static bool operator ==(Team left, Team right)
{
return Equals(left, right);
}
public static bool operator !=(Team left, Team right)
{
return !Equals(left, right);
}
Of course I am cannot reproduce that so it's just shot.

Implementing equality for 2d lines

I have simple class defining 2d line:
public class Line {
public double X1 { get; set; }
public double Y1 { get; set; }
public double X2 { get; set; }
public double Y2 { get; set; }
}
My primary goal is to get different lines from List using .Distinct(). In my case two lines are equal if theirs coordinates are equal regardless direction (line 1,2 -> 3,4 equals to 3,4 -> 1,2). I going to implement Equals like:
public override bool Equals(object obj) {
if (obj as Line == null) { return false; }
var second = (Line)obj;
if (this.X1 != second.X1 && this.X1 != second.X2) { return false; }
if (this.Y1 != second.Y1 && this.Y1 != second.Y2) { return false; }
if (this.X2 != second.X2 && this.X2 != second.X1) { return false; }
if (this.Y2 != second.Y2 && this.Y2 != second.Y1) { return false; }
return true;
}
but I have no idea how to implement GetHashCode (as I understand it's necessary to make it in case of using Distinct())

This becomes a bit easier if you first define a Point, then define your Line in terms of 2 Points.
Now, to calculate a reliable (but unaffected by direction) hash of a Line, make sure you order your points consistently when calculating the hash.
Putting this all together into a complete implementation (which also covers operator == and !=):
public class Point
{
public double X { get; set; }
public double Y { get; set; }
protected bool Equals(Point other)
{
return X.Equals(other.X) && Y.Equals(other.Y);
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj)) return false;
if (ReferenceEquals(this, obj)) return true;
if (obj.GetType() != this.GetType()) return false;
return Equals((Point) obj);
}
public override int GetHashCode()
{
unchecked
{
return (X.GetHashCode()*397) + Y.GetHashCode();
}
}
public static bool operator ==(Point left, Point right)
{
return Equals(left, right);
}
public static bool operator !=(Point left, Point right)
{
return !Equals(left, right);
}
}
public class Line
{
public Point Point1 { get; set; }
public Point Point2 { get; set; }
protected bool Equals(Line other)
{
return Equals(Point1, other.Point1) && Equals(Point2, other.Point2)
|| Equals(Point1, other.Point2) && Equals(Point2, other.Point1);
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj)) return false;
if (ReferenceEquals(this, obj)) return true;
if (obj.GetType() != this.GetType()) return false;
return Equals((Line) obj);
}
public override int GetHashCode()
{
unchecked
{
var orderedPoints =
new[] {Point1, Point2}.OrderBy(p => p != null ? p.X : 0)
.ThenBy(p => p != null ? p.Y : 0).ToList();
var p1 = orderedPoints[0];
var p2 = orderedPoints[1];
return ((p1 != null ? p1.GetHashCode() : 0)*397)
+ (p2 != null ? p2.GetHashCode() : 0);
}
}
public static bool operator ==(Line left, Line right)
{
return Equals(left, right);
}
public static bool operator !=(Line left, Line right)
{
return !Equals(left, right);
}
}