Select unique rows from a DataTable

The LINQ distinct select method is a powerful small method that can help you select unique entries from datatable.

The following example will return a datatable with unique results, from a datatable which can be populated from a database. The following example uses a datatable I created to show you how the LINQ distinct select method works.

The example below have a list of users, but I only want the 'user names' to be returned. They have to be unique, as I might want to use it in a report.

        /// <summary>
        /// Gets the user names.
        /// </summary>
        public static void GetUserNames()
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("UserId", typeof(int));
            dt.Columns.Add("UserName", typeof(string));
            dt.Rows.Add(1, "Joe Smith");
            dt.Rows.Add(2, "John Doe");
            dt.Rows.Add(3, "Joe Smith");
            dt.Rows.Add(4, "Jane Smith");
            dt.Rows.Add(5, "Jane Doe");

            DataTable filterTable = GetUniqueEntries(dt);

        }


        /// <summary>
        /// Gets the unique entries.
        /// </summary>
        /// <param name="dt">DataTable</param>
        /// <returns></returns>
        private static DataTable GetUniqueEntries(DataTable dt)
        {
            var query = (
            from row in dt.AsEnumerable()
            select row.Field<string>("UserName")).Distinct();

            DataTable dtDistinctNames = new DataTable();
            dtDistinctNames.Columns.Add("UserName", typeof(string));

            //have to return a datatable, thus loop through entries
            foreach (string item in query)
            {
                DataRow newRow = dtDistinctNames.NewRow();
                newRow["UserName"] = item;
                dtDistinctNames.Rows.Add(newRow);
            }

            return dtDistinctNames;
        }

This code snippet will return you a list of users where 'username' are unique. There eliminating duplicate names from the list. There are alternative ways to do this type of functionality - this blog entry is created to show you how easy it can be to use LINQ with C# code.