Find the count of duplicate items in a C# List

Question

I am using List in C#. Code is as mentioned below:

TestCase.cs

 public class TestCase
{
    private string scenarioID;
    private string error;

    public string ScenarioID
    {
        get
        {
            return this.scenarioID;
        }
        set
        {
            this.scenarioID = value;
        }
    }

    public string Error
    {
        get
        {
            return this.error;
        }
        set
        {
            this.error = value;
        }
    }

    public TestCase(string arg_scenarioName, string arg_error)
    {
        this.ScenarioID = arg_scenarioName;
        this.Error = arg_error;
    }
}

List I am createing is:

private List<TestCase> GetTestCases()
    {
        List<TestCase> scenarios = new List<TestCase>();
        TestCase scenario1 = new TestCase("Scenario1", string.Empty);
        TestCase scenario2 = new TestCase("Scenario2", string.Empty);
        TestCase scenario3 = new TestCase("Scenario1", string.Empty);
        TestCase scenario4 = new TestCase("Scenario4", string.Empty);
        TestCase scenario5 = new TestCase("Scenario1", string.Empty);
        TestCase scenario6 = new TestCase("Scenario6", string.Empty);
        TestCase scenario7 = new TestCase("Scenario7", string.Empty);

        scenarios.Add(scenario1);
        scenarios.Add(scenario2);
        scenarios.Add(scenario3);
        scenarios.Add(scenario4);
        scenarios.Add(scenario5);
        scenarios.Add(scenario6);
        scenarios.Add(scenario7);

        return scenarios;
    }

Now I am iterating through the list. I want to find the how many duplicate testcases are there in a list with same ScenarioID. Is there any way to solve it using Linq or any inbuilt method for List?

Regards, Priyank

Answer 1

Try this:

var numberOfTestcasesWithDuplicates = 
    scenarios.GroupBy(x => x.ScenarioID).Count(x => x.Count() > 1);

Answer 2

As a first idea:

int dupes = list.Count() - list.Distinct(aTestCaseComparer).Count();

Answer 3

To just get the duplicate count:

int duplicateCount = scenarios.GroupBy(x => x.ScenarioID)
                              .Sum(g => g.Count()-1);