I have two collections of following class
public class ABC
{
public int studentId {get;set;}
public int schoolId {get;set;}
// Class has other properties too both above two are the keys
}
Now i have two collections of ABC
ICollection<ABC> C1 = {Some Data}
ICollection<ABC> C2 = {Some Data}
I want to find objects of ABC in C1 that are not in C2 based on keys i-e StudentId and SchoolId
Use Except
var diff = C1.Except(C2)
Please also note, that in order to track equality you can override Equals method, or implement and pass IEqualityComparer to Except method
class ABCEqualityComparer : IEqualityComparer<ABC>
{
public bool Equals(ABC b1, ABC b2)
{
return (b1.studentId == b2.studentId) && (b1.schoolId == b2.schoolId)
}
public int GetHashCode(ABC b)
{
return 7*b.studentId.GetHashCode() + b.schoolId.GetHashCode();
}
}
Than you can use
var diff = C1.Except(C2, new ABCEqualityComparer())
Related
Thanks in advance. I can get required output when using var but i want to get required output by using Distinct in List<>.
InventoryDetails.cs
public class InventoryDetails
{
public int? PersonalInventoryGroupId { get; set; }
public int? PersonalInventoryBinId { get; set; }
}
InventoryController.cs
[HttpGet("GetInventory")]
public IActionResult GetInventory(int id)
{
//Below code will return distinct record
var inventory = (from i in _context.TempTbl
where i.TempId == id
select new
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).ToList().Distinct().ToList();
//Below code is not doing distinct
List<InventoryDetails> inventory = (from i in _context.TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).ToList().Distinct().ToList();
}
If i use var as return type, then i am able to get distinct records. Could some one assist it.
Please try like this it may help.
IList<InventoryDetails> inventory = _context.InventoryDetails.Where(x=>x.TempId == id).GroupBy(p => new {p.PersonalInventoryGroupId, p.PersonalInventoryBinId } )
.Select(g => g.First())
.ToList();
You need to override Equals and GetHashCode.
First, let's see the AnonymousType vs InventoryDetails
var AnonymousTypeObj1 = new { PersonalInventoryGroupId = 1, PersonalInventoryBinId = 1 };
var AnonymousTypeObj2 = new { PersonalInventoryGroupId = 1, PersonalInventoryBinId = 1 };
Console.WriteLine(AnonymousTypeObj1.Equals(AnonymousTypeObj2)); // True
var InventoryDetailsObj1 = new InventoryDetails { PersonalInventoryBinId = 1, PersonalInventoryGroupId = 1 };
var InvertoryDetailsObj2 = new InventoryDetails { PersonalInventoryBinId = 1, PersonalInventoryGroupId = 1 };
Console.WriteLine(InventoryDetailsObj1.Equals(InvertoryDetailsObj2)); // False
You can see the Equals behave differently which make Distinct behave differently. The problem is not var you mentioned in your question but AnonoymizeType
To make Distinct works as you expect, you need to override Equals and GetHashCode
public class InventoryDetails
{
public int? PersonalInventoryGroupId { get; set; }
public int? PersonalInventoryBinId { get; set; }
public override bool Equals(object obj)
{
if (obj == null) return false;
if (obj is InventoryDetails)
{
if (PersonalInventoryGroupId == (obj as InventoryDetails).PersonalInventoryGroupId
&& PersonalInventoryBinId == (obj as InventoryDetails).PersonalInventoryBinId)
return true;
}
return false;
}
public override int GetHashCode()
{
int hash = 17;
hash = hash * 23 + PersonalInventoryBinId.GetHashCode();
hash = hash * 23 + PersonalInventoryGroupId.GetHashCode();
return hash;
}
}
Another approach would be
List<InventoryDetails> inventory = (from i in TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).AsQueryable().ToList().Distinct(new customComparer()).ToList();
public class customComparer:IEqualityComparer<InventoryDetails>
{
public bool Equals(InventoryDetails x, InventoryDetails y)
{
if (x.TempId == y.TempId && x.PersonalInventoryBinId == y.PersonalInventoryBinId
&& x.PersonalInventoryGroupId == y.PersonalInventoryGroupId)
{
return true;
}
return false;
}
public int GetHashCode(InventoryDetails obj)
{
return string.Concat(obj.PersonalInventoryBinId.ToString(),
obj.PersonalInventoryGroupId.ToString(),
obj.TempId.ToString()).GetHashCode();
}
}
As said in a comment by Ivan, you make your life difficult by calling ToList before Distinct. This prevents the SQL provider from incorporating the Distinct call into the generated SQL statement. But that leaves the question: what causes the difference?
The first query generates anonymous type instances. As per the C# specification, by default anonymous types (in C#) are equal when their properties and property values are equal (structural equality). Conversely, by default, reference types (like InventoryDetails) are equal when their reference (say memory address) is equal (reference equality or identity). They can be made equal by overriding their Equals and GetHashcode methods, as some people suggested to do.
But that's not necessary if you remove the first ToList():
var inventory = (from i in _context.TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).Distinct().ToList();
Now the whole statement until ToList() is an IQueryable that can be translated into SQL. The SQL is executed and the database returns a distinct result set of raw records from which EF materializes InventoryDetails objects. The C# runtime code was even never aware of duplicates!
I want to query a list by Linq but filter by an other list containing two elements ( Name, Status) in my example.
This is inspired by an old question I've adapted to my issue.
LINQ: "contains" and a Lambda query
(in this answer it's working for only one element i.e. Status)
I try to use the "contains" method but didn't succeed to filter my list.
I should obtain a result with only two buildings (two, five)
Has anyone an idea where I'm stopped ?
Thanks
Blockquote
public class Building
{
public enum StatusType
{
open,
closed,
weird,
};
public string Name { get; set; }
public StatusType Status { get; set; }
}
private static readonly List<Building> BuildingList = new List<Building>()
{
new Building() {Name = "one", Status = Building.StatusType.open},
new Building() {Name = "two", Status = Building.StatusType.closed},
new Building() {Name = "three", Status = Building.StatusType.weird},
new Building() {Name = "four", Status = Building.StatusType.open},
new Building() {Name = "five", Status = Building.StatusType.closed},
new Building() {Name = "six", Status = Building.StatusType.weird},
};
private void GetResult()
{
var buildingSelect = new List<Building>
{
new Building() {Name = "two", Status = Building.StatusType.closed},
new Building() {Name = "five", Status = Building.StatusType.closed}
};
var q = (from building in BuildingList
where buildingSelect.Contains(building.Name, building.Status)
select building).ToList();
dataGridView1.DataSource = q;
}
The main problem of your LINQ is that you are trying the compare the equality of two Buildings, which LINQ can only compare by their references because Building does not implement IEquatable<Building> nor override object.Equals.
One way to solve it is to manually specify which properties to compare for equality as per #Wayne's answer.
The other way is, if Building instances are meant to be equated by their values and not by their references, implement IEquatable<Building> and override object.Equals:
public class Building : IEquatable<Building>
{
public Building(string name, StatusType status)
{
Name = name;
Status = status;
}
public enum StatusType
{
open,
closed,
weird,
};
public string Name { get; }
public StatusType Status { get; }
public static bool operator ==(Building left, Building right)
=> Equals(left, right);
public static bool operator !=(Building left, Building right)
=> !Equals(left, right);
public override bool Equals(object obj) => Equals(obj as Building);
public bool Equals(Building other)
{
if (ReferenceEquals(this, other))
{
return true;
}
if (ReferenceEquals(other, null) || GetType() != other.GetType())
{
return false;
}
return Name == other.Name && Status == other.Status;
}
public override int GetHashCode()
{
unchecked
{
int hash = 17;
hash = hash * 23 + Name?.GetHashCode() ?? 0;
hash = hash * 23 + Status.GetHashCode();
return hash;
}
}
}
That way, your original code would work because List.Contains will now use your implementation of IEquatable<Building> to check for equality.
You mean something like this?
var q = from b in BuildingList
from bs in buildingSelect
where b.Name == bs.Name && b.Status == bs.Status
select b;
or perhaps:
var q = from b in BuildingList
join bs in buildingSelect
on new { b.Name, b.Status } equals new { bs.Name, bs.Status }
select b;
You can either override the equality in the class itself, IF this makes sense.
Or just make the check normally with Any(), like this:
var q = (from building in BuildingList
where buildingSelect.Any(b => b.Name == building.Name
&& b.Status == building.Status)
select building).ToList();
This is a tricky one. I an trying to flatten a LINQ object collection. Each item in the collection has the potential of having two collections of other objects. See the example below.
public class DemoClass
{
public string Name {get; set;}
public string Address {get; set;}
public List<Foo> Foos = new List<Foo>();
public List<Bar> Bars = new List<Bars>();
}
What I had been doing is this using this code block to flatten this object
var output = from d in DemoClassCollection
from f in d.Foos
from b in d.Bars
select new {
d.Name,
d.Address,
f.FooField1,
f.FooField2,
b.BarField1,
b.BarField2
};
But the problem I'm having is that the result I get is only those DemoClass objects that have objects in the Foos and Bars collections. I need to get all objects in the DemoClass regardless if there are objects in the Foos and Bars collections.
Any help would be greatly appreciated.
Thanks!
Sounds like you might want to use DefaultIfEmpty:
var output = from d in DemoClassCollection
from f in d.Foos.DefaultIfEmpty()
from b in d.Bars.DefaultIfEmpty()
select new {
d.Name,
d.Address,
FooField1 = f == null ? null : f.FooField1,
FooField2 = f == null ? null : f.FooField2,
BarField1 = b == null ? null : b.BarField1,
BarField2 = b == null ? null : b.BarField2
};
Looks like a left outer join in Linq will work (http://msdn.microsoft.com/en-us/library/bb397895.aspx
var output = from d in DemoClassCollection
from f in d.Foos.DefaultIfEmpty()
from b in d.Bars.DefaultIfEmpty()
select new {
d.Name,
d.Address,
f.FooField1,
f.FooField2,
b.BarField1,
b.BarField2
};
I believe you can implement an IComparer to perform custom JOINS or UNIONS in linq based on how you implement the CompareTo() method
From MSDN: http://msdn.microsoft.com/en-us/library/system.icomparable.aspx
using System;
using System.Collections;
public class Temperature : IComparable
{
// The temperature value
protected double temperatureF;
public int CompareTo(object obj) {
if (obj == null) return 1;
Temperature otherTemperature = obj as Temperature;
if (otherTemperature != null)
return this.temperatureF.CompareTo(otherTemperature.temperatureF);
else
throw new ArgumentException("Object is not a Temperature");
}
public double Fahrenheit
{
get
{
return this.temperatureF;
}
set {
this.temperatureF = value;
}
}
public double Celsius
{
get
{
return (this.temperatureF - 32) * (5.0/9);
}
set
{
this.temperatureF = (value * 9.0/5) + 32;
}
}
}
public class CompareTemperatures
{
public static void Main()
{
ArrayList temperatures = new ArrayList();
// Initialize random number generator.
Random rnd = new Random();
// Generate 10 temperatures between 0 and 100 randomly.
for (int ctr = 1; ctr <= 10; ctr++)
{
int degrees = rnd.Next(0, 100);
Temperature temp = new Temperature();
temp.Fahrenheit = degrees;
temperatures.Add(temp);
}
// Sort ArrayList.
temperatures.Sort();
foreach (Temperature temp in temperatures)
Console.WriteLine(temp.Fahrenheit);
}
}
// The example displays the following output to the console (individual
// values may vary because they are randomly generated):
// 2
// 7
// 16
// 17
// 31
// 37
// 58
// 66
// 72
// 95
Table1:
ValueA
ValueB
ValueC
Example Data:
1,2,3
1,2,4
1,2,4
1,2,4
1,5,6
1,5,6
I want to get the unique rows based on these three values:
1,2,3
1,2,4
1,5,6
How can this be done most easily using linq?
Write your own IEqualityComparer and use Enumerable.Distinct on a collection of your objects representing the rows.
Something like (sorry, did not test in a compiler):
class Foo {
public int ValueA { get; set; }
public int ValueB { get; set; }
public int ValueC { get; set; }
}
class FooEqualityComparer : IEqualityComparer<Foo> {
public bool Equals(Foo x, Foo y) {
if(Object.ReferenceeEquals(x, y)) { return true; }
if(x == null || y == null) { return false; }
return x.ValueA == y.ValueA &&
x.ValueB == y.ValueB &&
x.ValueC == y.ValueC;
}
public int GetHashCode(Foo obj) {
if(obj == null) { return 0; }
unchecked {
int hashCode = 17;
hashCode = hashCode * 23 + obj.ValueA.GetHashCode();
hashCode = hashCode * 23 + obj.ValueB.GetHashCode();
hashCode = hashCode * 23 + obj.ValueC.GetHashCode();
return hashCode;
}
}
}
Then:
IEnumerable<Foo> foos = // some foos;
var distinct = foos.Distinct(new FooEqualityComparer());
you could use .Distinct() with your own comparer class
class MyComparer : IEqualityComparer<YourRowClass>
then use it like
yourList.Distinct(MyComparer())
I've got the following classes:
public class SupplierCategory : IEquatable<SupplierCategory>
{
public string Name { get; set; }
public string Parent { get; set; }
#region IEquatable<SupplierCategory> Members
public bool Equals(SupplierCategory other)
{
return this.Name == other.Name && this.Parent == other.Parent;
}
#endregion
}
public class CategoryPathComparer : IEqualityComparer<List<SupplierCategory>>
{
#region IEqualityComparer<List<SupplierCategory>> Members
public bool Equals(List<SupplierCategory> x, List<SupplierCategory> y)
{
return x.SequenceEqual(y);
}
public int GetHashCode(List<SupplierCategory> obj)
{
return obj.GetHashCode();
}
#endregion
}
And i'm using the following linq query:
CategoryPathComparer comparer = new CategoryPathComparer();
List<List<SupplierCategory>> categoryPaths = (from i in infoList
select
new List<SupplierCategory>() {
new SupplierCategory() { Name = i[3] },
new SupplierCategory() { Name = i[4], Parent = i[3] },
new SupplierCategory() { Name = i[5], Parent = i[4] }}).Distinct(comparer).ToList();
But the distinct does not do what I want it to do, as the following code demonstrates:
comp.Equals(categoryPaths[0], categoryPaths[1]); //returns True
Am I using this in a wrong way? why are they not compared as I intend them to?
Edit:
To demonstrate the the comparer does work, the following returns true as it should:
List<SupplierCategory> list1 = new List<SupplierCategory>() {
new SupplierCategory() { Name = "Cat1" },
new SupplierCategory() { Name = "Cat2", Parent = "Cat1" },
new SupplierCategory() { Name = "Cat3", Parent = "Cat2" }
};
List<SupplierCategory> list1 = new List<SupplierCategory>() {
new SupplierCategory() { Name = "Cat1" },
new SupplierCategory() { Name = "Cat2", Parent = "Cat1" },
new SupplierCategory() { Name = "Cat3", Parent = "Cat2" }
};
CategoryPathComparer comp = new CategoryPathComparer();
Console.WriteLine(comp.Equals(list1, list2).ToString());
Your problem is that you didn't implement IEqualityComparer correctly.
When you implement IEqualityComparer<T>, you must implement GetHashCode so that any two equal objects have the same hashcode.
Otherwise, you will get incorrect behavior, as you're seeing here.
You should implement GetHashCode as follows: (courtesy of this answer)
public int GetHashCode(List<SupplierCategory> obj) {
int hash = 17;
foreach(var value in obj)
hash = hash * 23 + obj.GetHashCode();
return hash;
}
You also need to override GetHashCode in SupplierCategory to be consistent. For example:
public override int GetHashCode() {
int hash = 17;
hash = hash * 23 + Name.GetHashCode();
hash = hash * 23 + Parent.GetHashCode();
return hash;
}
Finally, although you don't need to, you should probably override Equals in SupplierCategory and make it call the Equals method you implemented for IEquatable.
Actually, this issue is even covered in documentation:
http://msdn.microsoft.com/en-us/library/bb338049.aspx.