How to find the duplication from the list using either LINQ or Loop in C#

Question

I have the list. i want to return true if any duplicates found.

for example, below is the list

List<string> Listvalues = new List<string> {"E-10-XN-PP" , E-10-XN-MM, E-10-XN-MM}; ==> Found duplicates

List<string> Listvalues = new List<string> {"E-10-XN-PP" , E-10-XN-MM, E-10-XN-NM}; ==> No duplicates found

How to check the duplicates or no duplicates using LINQ or Loop in C#?

Answer 1

You can try something like this to see if a list of string has duplicates

    public static  bool ListHasDuplicates(List<string> lst)
    {
        bool result = false;
        var distinctList = lst.Distinct().ToList();
        result = (lst.Count() == distinctList.Count());
        return !result;
    }

Answer 2

Hello,

The following uses C#9 new expressions e.g. List<string> listValues = new () rather than List<string> listValues = new List<string>()

The following uses a language extension.

public static class Extensions
{
    public static bool HasDuplications(this List<string> sender) => 
        sender.GroupBy(value => value).Any(@group => @group.Count() > 1);
    public static string ToYesNoString(this bool value) => value ? "Yes" : "No";
}

First we get yes then no.

List<string> listValues = new ()
{
    "E-10-XN-PP", 
    "E - 10 - XN - MM", 
    "E - 10 - XN - MM"
};

Debug.WriteLine(listValues.HasDuplications().ToYesNoString());

listValues.RemoveAt(1);

Debug.WriteLine(listValues.HasDuplications().ToYesNoString());