Filter List from comparing two List with some condition

[PWC]

I want to prepare a list of type CampaignDetails after comparing the two list together through Linq. You can see code snippet below:\[code\]var str = service.GetActiveCampaignBySubCatId(lang, subCatId); // List1var sploffer = service.GetSpecialOfferCampaignsForMobile(lang); // List2List<CampaignDetails> CampList = new List<CampaignDetails>();foreach (var data in str){ var CampL = (from offer in sploffer where offer.CampaignId != data.CampaignId select offer).ToList(); CampList.Add(CampL); // getting red mark here}\[/code\]Whats going wrong here. I am unable to filter the list based on above code snippet.