How to get the distinct elements?

Question

I have a class as under

class WarningClass
    {
        public string SqlEyeWarning { get; set; }
        public string FileName { get; set; }
    }

It is populated as under

List<WarningClass> lstWarningClass1 = new List<WarningClass>();
lstWarningClass1.Add(new WarningClass { FileName = "a.sql", SqlEyeWarning = "SD001: order mismatch or it should be ON." });
lstWarningClass1.Add(new WarningClass { FileName = "a.sql", SqlEyeWarning = "SD001: order mismatch or it should be ON." });
lstWarningClass1.Add(new WarningClass { FileName = "c.sql", SqlEyeWarning = "SD009: Missing or order mismatch of Grant statement." });

As can be make out that there is a duplicate entry for the first and second record.

How to get unique entries.

Final output

FileName = "a.sql", SqlEyeWarning = "SD001: order mismatch or it should be ON." 
FileName = "c.sql", SqlEyeWarning = "SD009: Missing or order mismatch of Grant statement."

If I do lstWarningClass1.Distinct(), that does not work

Implement the `IEquatable` interface, and the `District` method will probably work. — SimpleVar, Jun 06 '13 at 02:42

score 3 · Answer 1 · answered Jun 06 '13 at 02:44

Linq's Distinct() has the following in its description:

The default equality comparer, Default, is used to compare values of the types that implement the IEquatable generic interface. To compare a custom data type, you need to implement this interface and provide your own GetHashCode and Equals methods for the type.

Do the bolded part and Distinct() will work.

Steven Wexler · Accepted Answer · 2013-06-06T03:24:52.473

1

You could use IEnumerable.GroupBy to group the objects in the list by the criteria that you care about. Then, you can select the first element of each group.

You can group by FileName like so:

lstWarningClass1.GroupBy(w => w.FileName).Select(g => g.First())

or by FileName and SqlEyeWarning like so:

lstWarningClass1.GroupBy(w => new {w.FileName, w.SqlEyeWarning}).Select(g => g.First())

edited Jun 06 '13 at 03:24

answered Jun 06 '13 at 02:43

Steven Wexler

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Mind explaining what you're doing a bit? Your answer will be more helpful that way. – Brad Koch Jun 06 '13 at 03:07
Also, it doesn't seem that he is grouping my `FileName` only, but all properties. – SimpleVar Jun 06 '13 at 03:10
@YoryeNathan That may be true, but the example he gave was ambiguous. I'll amend my answer to include grouping by multiple properties. – Steven Wexler Jun 06 '13 at 03:13

score 1 · Answer 3 · answered Jun 06 '13 at 03:18

You need to create a customize IEqualityComparer<T>:

public class CustomComparer : IEqualityComparer<WarningClass>
{
    public bool Equals(WarningClass x, WarningClass y)
    {
        return x.SqlEyeWarning.Equals(y.SqlEyeWarning)
               && x.FileName.Equals(y.FileName);
    }

    public int GetHashCode(WarningClass obj)
    {
        return obj.FileName.GetHashCode() 
            ^ obj.SqlEyeWarning.GetHashCode();
    }
}

Then call overloaded Distinct method with your customize comparer:

var result = lstWarningClass1.Distinct(new CustomComparer());

How to get the distinct elements?

3 Answers3