C# 集合合并条目

Question

    public class Contact
    {
        public string Name { get; set; }
        public string Fax { get; set; }
        public string Email {get; set; }
    }

如果我有一个如下所示的联系人列表:

List<Contact> contactList = 
╔═════╦══════╦═════════════╗
║Name ║ Fax  ║ Email       ║
╠═════╬══════╬═════════════╣
║  a  ║ 1    ║             ║
║  b  ║      ║ b@email.com ║
║  c  ║ 3    ║ c@email.com ║
║  a  ║      ║ a@email.com ║           
║  b  ║ 2    ║             ║
╚═════╩══════╩═════════════╝

如何组合具有相同名称的条目并产生此结果？

╔═════╦══════╦═════════════╗
║Name ║ Fax  ║ Email       ║
╠═════╬══════╬═════════════╣
║  a  ║ 1    ║ a@email.com ║
║  b  ║ 2    ║ b@email.com ║
║  c  ║ 3    ║ c@email.com ║
╚═════╩══════╩═════════════╝

这是我到目前为止尝试过的:

var result = contactList.Select(contact => contact.Name)
                             .Distinct()
                             .Select(name => contactList.First(contact => contact.Name == name))
                             .ToList();


 foreach (var contact in contactList)
            {
                var c = result.First(r => r.Name == contact.Name);
                c.Name = string.IsNullOrWhiteSpace(contact.Name) ? c.Name : contact.Name;
                c.Fax = string.IsNullOrWhiteSpace(contact.Fax ? c.Fax : contact.Fax;
                c.Email = string.IsNullOrWhiteSpace(contact.Email) ? c.Email : contact.Email;
            }

有没有更有效的方法？

Answer 1

看起来您需要执行GroupBy，然后我假设这些值是空值，因此您只想获取第一个非空值。

var results = (from contact in constactList
               group contact by contact.Name into contacts
               select new Contact
               {
                   Name = contacts.Key,
                   Fax = contacts.FirstOrDefault(c => c.Fax != null)?.Fax,
                   Email = contacts.FirstOrDefault(c => c.Email != null)?.Email 
               }).ToList();

或者在方法语法中

var results = constactList.GroupBy(contact => contact.Name)
    .Select(contacts => new Contact
    {
        Name = contacts.Key,
        Fax = contacts.FirstOrDefault(c => c.Fax != null)?.Fax,
        Email = contacts.FirstOrDefault(c => c.Email != null)?.Email 
    }).ToList();

或者如果它们是空白字符串，您也可以这样做

Fax = contacts.FirstOrDefault(c => !string.IsNullOrWhiteSpace(c.Fax))?.Fax

如果您没有 C# 6，则执行以下操作

Fax = contacts.Where(c => !string.IsNullOrWhiteSpace(c.Fax)).Select(c => c.Fax).FirstOrDefault()