Group next class by field CompanyId and only add all CampaignId in a list Linq lambda public class ReportWeeklyDTO { public string CampaignId { get; set; } public string CampaignName { get; set; } public int NumberMessages { get; set; } public string User { get; set; } public int SentMessages { get; set; } public int ErrorMessages { get; set; } public string ErrorDescription { get; set; } public string CompanyId { get; set; } }