如何按字段对列表进行排序

Question

美好的一天 4 你们

我有一个对象列表

我的对象就像

Product = "iPhone"; 
Category = "SmartPhone";

Product = "HP"; 
Category = "PC";

Product = "HTC"; 
Category = "SmartPhone";

我将每个对象插入到我的测试中所以它就像

List<Myobject> MyList = new List<Myobject>();

现在我需要按类别排序/排序我的列表

因为我需要我的列表首先显示智能手机类别然后显示其他类别

Answer 1

您可以使用 List.Sort

l.Sort((p, q) => p.Category.CompareTo(q.Category));

相对于 LINQ OrderBy 的优势在于，您可以就地对列表进行排序，而不是生成一个 IOrderedEnumerable那么你必须在 List 中重新转换。

Answer 2

查看 LINQ OrderBy 扩展方法。

MyList.OrderBy (p => p.Category);

如果您需要更复杂的方式对类别进行排序，您可以创建一个实现 IComparer 接口的类，并在其中实现排序逻辑。

        public class SmartphonesFirst : IComparer<Product>
        {
            const string Smartphone = "Smartphone";

            public int Compare( Product x, Product y )
            {
                if( x.Category == Smartphone && y.Category != Smartphone )
                {
                    return -1;
                }
                if( y.Category == Smartphone && x.Category != Smartphone )
                {
                    return 1;
                }
                else
                {
                    return Comparer<String>.Default.Compare (x.Category, y.Category);
                }
            }
        }

您可以不使用 LINQ 来完成此操作：

            var l = new List<Product> ();
            l.Add (new Product ()
            {
                Name = "Omnia 7",
                Category = "Smartphone"
            });

            l.Add (new Product ()
            {
                Name = "Mercedes",
                Category = "Car"
            });

            l.Add (new Product ()
            {
                Name = "HTC",
                Category = "Smartphone"
            });

            l.Add (new Product ()
            {
                Name = "AMD",
                Category = "CPU"
            });

            l.Sort (new SmartphonesFirst ());

            foreach( var p in l )
            {
                Console.WriteLine (String.Format ("{0} : {1}", p.Category, p.Name));
            }

或者使用 LINQ：

            var l = new List<Product> ();
            l.Add (new Product ()
            {
                Name = "Omnia 7",
                Category = "Smartphone"
            });

            l.Add (new Product ()
            {
                Name = "Mercedes",
                Category = "Car"
            });

            l.Add (new Product ()
            {
                Name = "HTC",
                Category = "Smartphone"
            });

            l.Add (new Product ()
            {
                Name = "AMD",
                Category = "CPU"
            });

            var sorted = l.OrderBy (p => p, new SmartphonesFirst ());

            foreach ( var p in sorted )
            {
                Console.WriteLine (String.Format ("{0} : {1}", p.Category, p.Name));
            }

Answer 3

您可以使用 Sort 方法和自定义比较，按类别（降序）排序，然后按产品（升序）排序：

MyList.Sort((a, b) => {
  // compare b to a to get descending order
  int result = b.Category.CompareTo(a.Category);
  if (result == 0) {
    // if categories are the same, sort by product
    result = a.Product.CompareTo(b.Product);
  }
  return result;
});

如果您想单独列出智能手机，然后升序排序：

MyList.Sort((a, b) => {
  int result = (a.Category == "SmartPhone" ? 0 : 1) - (b.Category == "SmartPhone" ? 0 : 1);
  if (result == 0) {
    result = a.Category.CompareTo(b.Category);
    if (result == 0) {
      result = a.Product.CompareTo(b.Product);
    }
  }
  return result;
});