如何按字段对列表进行排序

Question

大家好4

我有一个对象列表

我的对象喜欢

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，就像这样

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

现在我需要按类别对 MyList 进行排序

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

的优点是，您可以就地对列表进行排序，而不是生成

IOrderedEnumerable<T>

，然后您必须在

List<T>

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 来做到这一点：

            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;
});

如果您想挑出智能手机，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;
});