How to merge 2 List<T> and removing duplicate values from it in C#

I have two lists List that I need to combine in third list and remove duplicate values from that lists

A bit hard to explain, so let me show an example of what the code looks like and what I want as a result, in sample I use int type not ResultAnalysisFileSql class.

first_list = [1, 12, 12, 5]

second_list = [12, 5, 7, 9, 1]

The result of combining the two lists should result in this list: resulting_list = [1, 12, 5, 7, 9]

You'll notice that the result has the first list, including its two "12" values, and in second_list has an additional 12, 1 and 5 value.

ResultAnalysisFileSql class

[Serializable]
    public partial class ResultAnalysisFileSql
    {
        public string FileSql { get; set; }

        public string PathFileSql { get; set; }

        public List<ErrorAnalysisSql> Errors { get; set; }

        public List<WarningAnalysisSql> Warnings{ get; set; }

        public ResultAnalysisFileSql()
        {

        }

        public ResultAnalysisFileSql(string fileSql)
        {
            if (string.IsNullOrEmpty(fileSql)
                || fileSql.Trim().Length == 0)
            {
                throw new ArgumentNullException("fileSql", "fileSql is null");
            }

            if (!fileSql.EndsWith(Utility.ExtensionFicherosErrorYWarning))
            {
                throw new ArgumentOutOfRangeException("fileSql", "Ruta de fichero Sql no tiene extensión " + Utility.ExtensionFicherosErrorYWarning);
            }

            PathFileSql = fileSql;
            FileSql = ObtenerNombreFicheroSql(fileSql);
            Errors = new List<ErrorAnalysisSql>();
            Warnings= new List<WarningAnalysisSql>();
        }
         
        private string ObtenerNombreFicheroSql(string fileSql)
        {
            var f = Path.GetFileName(fileSql);
            return f.Substring(0, f.IndexOf(Utility.ExtensionFicherosErrorYWarning));
        }


        public override bool Equals(object obj)
        {
            if (obj == null)
                return false;
            if (!(obj is ResultAnalysisFileSql))
                return false;

            var t = obj as ResultAnalysisFileSql;
            return t.FileSql== this.FileSql
                && t.PathFileSql == this.PathFileSql
                && t.Errors.Count == this.Errors.Count
                && t.Warnings.Count == this.Warnings.Count;
        }


    }

Any sample code for combine and removing duplicates ?

Have you had a look at Enumerable.Union

> This method excludes duplicates from the return set. This is different > behavior to the Concat > method, which returns all the elements > in the input sequences including > duplicates.

List<int> list1 = new List<int> { 1, 12, 12, 5};
List<int> list2 = new List<int> { 12, 5, 7, 9, 1 };
List<int> ulist = list1.Union(list2).ToList();

// ulist output : 1, 12, 5, 7, 9

why not simply eg

var newList = list1.Union(list2)/*.Distinct()*//*.ToList()*/;

oh ... according to the documentation you can leave out the .Distinct()

> This method excludes duplicates from > the return set

Union has not good performance : this article describe about compare them with together

var dict = list2.ToDictionary(p => p.Number);
foreach (var person in list1)
{
        dict[person.Number] = person;
}
var merged = dict.Values.ToList();

Lists and LINQ merge: 4820ms
Dictionary merge: 16ms
HashSet and IEqualityComparer: 20ms
LINQ Union and IEqualityComparer: 24ms

Use Linq's Union:

using System.Linq;
var l1 = new List<int>() { 1,2,3,4,5 };
var l2 = new List<int>() { 3,5,6,7,8 };
var l3 = l1.Union(l2).ToList();

    List<int> first_list = new List<int>() {
        1,
        12,
        12,
        5
    };

    List<int> second_list = new List<int>() {
        12,
        5,
        7,
        9,
        1
    };

    var result = first_list.Union(second_list);