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List Class

Posted on 2012-12-20
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Last Modified: 2013-01-05
Hi,

I have implemented a class that is a list:

Public class CompareItems
{
      Public string type {get; set; }
      Public int item1 { get; set; }
      Public int item2 { get; set; }
}

Public List< CompareItems> compareJobList = new List< CompareItems>();

I can populate this okay, but I now have a requirement to check that the list does not accept duplicate values.  I know this could be done on normal list by using the contains function.

However can it be done on this type of a list?

So I would need to check all 3 values don't exist?
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Question by:andyw27
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5 Comments
 
LVL 18

Expert Comment

by:dj_alik
ID: 38710377
If you're using .NET 3.5 or later, LINQ is the answer to this one:
compareJobList .Where(t => t.item1 == 3);
0
 
LVL 18

Expert Comment

by:dj_alik
ID: 38710391
if  less .net 3.5
compareJobList .Exists(t => t.item1 == 3&& t.item2=1)
or
compareJobList .FindAll(t => t.item1 == 3&& t.item2=1)
0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 38710483
If you're using .NET 3.5 or later, LINQ is the answer to this one:
compareJobList .Where(t => t.item1 == 3);
I'd suggest Any instead of Where.

using System.Linq;

...

bool exists = compareJobList .Any(t => t.item1 == 3);

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0
 
LVL 55

Expert Comment

by:Jaime Olivares
ID: 38711936
Instead of a List<> you can use a HashSet<> (http://msdn.microsoft.com/en-us/library/bb359438.aspx)
A hashset will never store a duplicate
0
 
LVL 29

Accepted Solution

by:
Göran Andersson earned 2000 total points
ID: 38712372
To be able to check if an item is in a collection, you need to be able to compare them. The default comparison for objects only compares the references, so if you have two objects with the exact same values, they will still not be equal.

Implement the IEquatable<T> interface for the class:

public class CompareItems : IEquatable<CompareItems> {
	public string type { get; set; }
	public int item1 { get; set; }
	public int item2 { get; set; }

	public bool Equals(CompareItems other) {
		return type == other.type && item1 == other.item1 && item2 == other.item2;
	}

}

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Now you can check if an item exists in the list. In this example, only the first item will be added to the list:

CompareItems item1 = new CompareItems { type = "test", item1 = 42, item2 = 1337 };
if (!compareJobList.Contains(item1)) {
	compareJobList.Add(item1);
}

CompareItems item2 = new CompareItems { type = "test", item1 = 42, item2 = 1337 };
if (!compareJobList.Contains(item2)) {
	compareJobList.Add(item2);
}

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