Linq distinct not working correctly

Question

I\'m having a strange problem with a linq query. I\'m using LINQPad 4 to make some a query that uses regular expression using LinqToSQL as the LinqPad driver.

Here\'

Answer 1

var result = from eachError in SystemErrors
             let match = Regex.Match(eachError.Description, "...")
             group eachError by new 
             {
              FamilyCode = match.Groups["FamilyCode"].Value,
              ProductPrefix = match.Groups["ProductPrefix"].Value,
              BillingGroup = match.Groups["BillingGroup"].Value,
              Debtor = match.Groups["Debtor"].Value
             }
             into unique
             select unique.key;

When you use Distinct(), it's distinct by pointer to each object, not value because select new {} is object type not value type. Try using group by instead.

Answer 2

On the other hand, you can use .Distinct(IEqualityComparer<T>) overload and provided EqualityComparer for the object that you want to process.