c# - 使用 LINQ 计算列表中项目的出现次数

Question

我正在尝试使用 LINQ 计算列表中某项的出现次数，

我有以下架构-

用户(提供的所有条目)，计数(待计算)

计数应该像 -

我想不出一个优雅的解决方案。

是否可以只使用 LINQ？如果没有，我们如何使用带有一些 C# 代码的 LINQ 来实现这一点。

Answer 1

您可以结合使用循环和 Enumerable.Take 来做到这一点, 像这样的东西:

for (int i = 0; i < list.Count; i++)
{
    //Get count of current element to before:
    int count = list.Take(i+1)
                    .Count(r => r.UserName == list[i].UserName);
    list[i].Count = count;
}

您的 list 定义为:

List<User> list = new List<User>
    {
        new User{UserName = "A"},
        new User{UserName = "B"},
        new User{UserName = "A"},
        new User{UserName = "A"},
        new User{UserName = "B"},
        new User{UserName = "A"},
        new User{UserName = "C"},
        new User{UserName = "A"},

    };

和 User 类为:

public class User
{
    public string UserName { get; set; }
    public int Count { get; set; }
}

稍后您可以像这样打印输出:

foreach (var item in list)
{
    Console.WriteLine("UserName: {0}, Running Total: {1}", item.UserName, item.Count);
}

你会得到:

UserName: A, Running Total: 1
UserName: B, Running Total: 1
UserName: A, Running Total: 2
UserName: A, Running Total: 3
UserName: B, Running Total: 2
UserName: A, Running Total: 4
UserName: C, Running Total: 1
UserName: A, Running Total: 5