System.OutOfMemoryException using linq C#

Hi All,

Please resolve this issue .  

It contains around 30000 records. When grouping using Linq to list. It throws error of System.OutOfMemoryException

var resultdt = dt.GroupBy(test => new { test.CompanyName, test.MainTelNumber, test.Address, test.Address2, test.City, test.State, test.ZipCode, test.EventCity, test.JobCategory, test.WebsiteURL, test.EventState })
.Select(grp => grp.First())
.ToList();