Question

如何通过其MemberRole排序下面的客户列表，例如Golden先是Silver，其余的是他们的Firstname＆amp;姓氏。

public class  Customer
{
    public string id { get; set; }
    public string Firstname { get; set; } 
    public string Lastname { get; set; }
    public string memberRole { get; set; } // Golden and Silver 
}

List<Customer> customers = new List<Customer>();

Answer 1

您OrderByDescending可以使用true 而不是false的布尔值：

customers = customers .OrderByDescending(c => c.memberRole == "Golden") .ThenBy(c => c.Firstname) .ThenBy(c => c.LastName) .ToList();

Answer 2

customers.OrderBy(c => 
   c.memberRole == "Golden" ? 0 : (c.memberRole == "Silver" ? 1 : 2))
 .ThenBy(c => c.FirstName)
 .ThenBy(c => c.LastName)

Answer 3

从设计的角度来看，最好将成员角色比较放入单独的类中。这样，如果出现新角色，您可以轻松地重复使用它，进行单元测试和升级。对于LINQ兼容性，最好实现IComparer类。

public class MemberRoleComparison : IComparer<string>
{
    // Put in required order from most importan to less
    internal static readonly string[] ROLES = { "Golden", "Silver", "Bronze" };

    int IComparer<string>.Compare(string x, string y)
    {
        return Array.IndexOf(ROLES, x).CompareTo(Array.IndexOf(ROLES, y));
    }
}

然后排序看起来像：

var sorted = customers
    .OrderBy(item => item.memberRole, new MemberRoleComparison())
    .ThenBy(c => c.Firstname)
    .ThenBy(c => c.Lastname)
;

如果可以通过规范，您可能希望用枚举替换角色的字符串表示。

public enum MemberRole
{
    Golden = 1,
    Silver = 2,
    Bronze = 3
}

然后，您可以直接比较角色，例如＆＃34; customer1.memberRole＆gt; customer2.memberRole＆＃34;

如果要优化速度和内存消耗（通常快30-40％），最好使用List.Sort例程。首先定义客户比较可重用类：

public class CustomerComparison : IComparer<Customer>
{
    private IComparer<string> _RoleComparer = new MemberRoleComparison();

    int IComparer<Customer>.Compare(Customer x, Customer y)
    {
        int result = _RoleComparer.Compare(x.memberRole, y.memberRole);
        result = result == 0 ? string.Compare(x.Firstname, y.Firstname) : result;
        return result == 0 ? string.Compare(x.Lastname, y.Lastname) : result;
    }
}

然后只使用现有列表的Sort方法：

customers.Sort(new CustomerComparison());

但是为了获得更好的性能，您可能希望使用并行化的LINQ：

var sorted = customers
    .AsParallel()
    .OrderBy(item => item.memberRole, new MemberRoleComparison())
    .ThenBy(c => c.Firstname)
    .ThenBy(c => c.Lastname)
;

Answer 4

var result = customers
    .Select(z => new
        {
            OrderableRole = role == "Golden"
                ? 1
                : role == "Silver"
                    ? 2
                    : int.MaxValue,
            Customer = z
        })
    .OrderBy(z => z.OrderableRole)
    .ThenBy(z => z.Customer.Firstname)
    .ThenBy(z => z.Customer.LastName)
    .ToList();

如何排序列表？

4 个答案: