How to find List has duplicate values in List<string>

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I have a list object objList with two list of values

C#

foreach (object eachItem in objList )
       {
       }

How to find any duplicate value is there inside the objList

Posted 14-Dec-14 22:09pm

MAGuru

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2 solutions

Solution 1

var duplicateByLinq = objList.GroupBy(x=>x).Where(x=>x.Count() >1).Select(group=>Group.Key));

Posted 14-Dec-14 22:13pm

Member 8118083

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OriginalGriff · Accepted Answer · 2014-12-14T22:17:00

There are a number of ways to do this, and the easiest is to use Linq.
But...since you seem to be a beginner you may not have reached that yet, and it's pretty simple to find duplicates if you think about it for a moment.
The List<T> collection has a Sort method[^], and if you order your values then duplicates will be next to each other:

C#

List<string> objList = new List<string>() {"A", "C", "B", "Z", "B"};
obList.Sort();

Once they are sorted, duplicates are next to each other, so it's a simple matter to find duplicates:

C#

string last = "";
foreach (object eachItem in objList )
    {
    if (eachItem == last)
        {
        Console.WriteLine("Duplicate: {0}", eachItem);
        }
    last == eachItem;
    }