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,就像它一样

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

现在我需要根据类别对MyList进行sord/order

因为我需要我的列表首先显示SmartPhone类别然后是其他类别

Answer 1

您可以使用List.Sort

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

LINQ的优势OrderBy在于,您可以就地排序列表,而不是生成一个IOrderedEnumerable<T>,然后您必须在a中重新转换List<T>.

Answer 2

查看LINQ OrderBy扩展方法.

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

如果需要更复杂的方法对类别进行排序,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);
                }
            }
        }

你可以不使用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;
});

如果你想挑出智能手机,然后按升序排序:

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;
});