How to remove (via linq) duplicates from a List of objects

Question

My main object, has a property which is a List of tags

    [SharedCosmosCollection("shared")]
    public class GlobalPageTemplate : ISharedCosmosEntity
    {
        /// <summary>
        /// Id
        /// </summary>
        [JsonProperty("Id")]
        public string Id { get; set; }

        /// <summary>
        /// Cosmos Entity name
        /// </summary>
        [CosmosPartitionKey]
        public string CosmosEntityName { get; set; }

        /// <summary>
        /// Page name
        /// </summary>
        public string ExtractedPageName { get; set; }

        /// <summary>
        /// Site collection Template Name
        /// </summary>
        public string ExtractedSitecollectionTemplateName { get; set; }

        /// <summary>
        /// GlobalDesignTenantId
        /// </summary>
        public string ExtractedGlobalDesignTenantId { get; set; }

        /// <summary>
        /// Global design tenant site collection url
        /// </summary>
        public string ExtractedGlobalDesigntenantSiteCollectionUrl { get; set; }


        /// <summary>
        /// Page template picture Url
        /// </summary>
        public string PageTemplatePictureUrl { get; set; }

        /// <summary>
        /// Base64 image of the page template
        /// </summary>
        public string Base64Image { get; set; }

        /// <summary>
        /// Name of the template
        /// </summary>
        public string PageTemplateName { get; set; }


        /// <summary>
        /// Page sections
        /// </summary>
        public List<Section> Sections { get; set; }

        /// <summary>
        /// Tags
        /// </summary>
        public List<Tag> Tags { get; set; }
    }

Tag object is here:

 public class Tag : ISharedCosmosEntity
    {
        /// <summary>
        /// Id
        /// </summary>
        [JsonProperty("Id")]
        public string Id { get; set; }
        /// <summary>
        /// Tag name
        /// </summary>
        public string TagName { get; set; }
        /// <summary>
        /// cosmos entity name
        /// </summary>
        [CosmosPartitionKey]
        public string CosmosEntityName { get; set; }
    }

In my WebAPI, from the frontend, I might get duplicate tags,

how do I remove them and leave a clean list of tags before saving?

Answer 1

Not exactly an answer to your question (the other answers are all valid solutions for that), but if for some reason you're looking to actually extract your duplicate objects, such as for debugging, error processing, whatever, I wanted to offer the below.

var duplicates = someList
  .GroupBy(r => r.Id)
  .Where(g => g.Count() > 1)
  .ToList();

Then you have a slightly different way to manage your list from pure distinct

someList = someList.Except(duplicates).ToList();

Which is then a list of keys which had no duplicates.