集合對象去重

    public class Compare<T, C> : IEqualityComparer<T>
    {
        private Func<T, C> _getField;
        public Compare(Func<T, C> getfield)
        {
            this._getField = getfield;
        }
        public bool Equals(T x, T y)
        {
            return EqualityComparer<C>.Default.Equals(_getField(x), _getField(y));
        }
        public int GetHashCode(T obj)
        {
            return EqualityComparer<C>.Default.GetHashCode(this._getField(obj));
        }
    }

Compare

  public static class CommonHelper
    {
        /// <summary>
        /// 自定義Distinct擴展方法
        /// </summary>
        /// <typeparam name="T">要去重的對象類</typeparam>
        /// <typeparam name="C">自定義去重的字段類型</typeparam>
        /// <param name="source">要去重的對象</param>
        /// <param name="getfield">獲取自定義去重字段的委託</param>
        /// <returns></returns>
        public static IEnumerable<T> MyDistinct<T, C>(this IEnumerable<T> source, Func<T, C> getfield)
        {
            return source.Distinct(new Compare<T, C>(getfield));
        }
    }

//定義一個類繼承IEqualityComparer接口
    public class ModelComparer : IEqualityComparer<Model>
    {
        public bool Equals(Model x, Model y)
        {
            return x.Title.ToUpper() == y.Title.ToUpper();
        }
        public int GetHashCode(Model obj)
        {
            return obj.Title.ToUpper().GetHashCode();
        }
    }

modelList = modelList.Distinct(new ModelComparer()).ToList();

var title = modelList.GroupBy(m => m.Title.ToLower().Trim()).Select(m => new { ID = m.FirstOrDefault().ID });
            modelList = modelList.Where(m => title.Select(mo => mo.ID).Contains(m.ID)).ToList(); 
            foreach (var item in modelList)
            {
                Console.WriteLine(item.ID + "\t" + item.Title);
            }