使用 LINQ-to-Objects 有条件地合并两个集合

Question

我需要帮助找到使用 LINQ-to-Objects 合并两个内存中集合的最有效方法。就我而言，这不是简单的连接或连接，因为需要根据属性值排除某些项目。

让我们使用以下示例（不太现实，但它说明了我的需要）：

public abstract class Person
{
    public String Name { get; set; }
}

public class Employee : Person
{
    public DateTime? TerminationDate { get; set; }
}

public class Customer : Person
{
    ...
}

注意，员工也可能是客户。

我有一个员工列表和一个客户列表，并希望生成遵循以下规则的所有人员的列表：

1. 所有不属于员工的客户
2. 所有不属于客户且未终止的员工 (TerminationDate == null)
3. 所有人员既是客户又是员工并且没有终止 (TerminationDate == null)

实现此目的最有效的方法是什么？

Answer 1

很难确定，但假设乔恩对姓名匹配的猜测是正确的，那么这在概念上有意义吗？

请注意，它当前执行多次迭代，因此我通常会在某些地方添加 ToArray 等，但我不想在尝试验证概念位时将其添加到此代码中。

var allPeople = ...;

var customers = allPeople.OfType<Customer>();
var employees = allPeople.OfType<Employee>();

var employeeNames = new HashSet(employees.Select(p => p.Name));
var customerNames = new HashSet(employees.Select(p => p.Name));

// list item #1
var customersNotEmployees = customers
    .Where(c => employeeNames.Contains(c.Name) == false);

// will be used by #2 and #3
var employeesNotTerminated = employees
    .Where(e => e.TerminationDate == null);

// list item #2
var employeesNotCustomersAndNotTerminated = employeesNotTerminated
    .Where(e => customerNames.Contains(e.Name) == false);

// list item #3
var employeesAndCustomersAndNotTerminated = employeesNotTerminated
    .Where(e => customerNames.Contains(e.Name) == true);

Answer 2

虽然不一定不正确，但詹姆斯的示例比我希望的要复杂一些，并且不完整，因为我需要一个列表作为最终结果。

也不确定这是否是最好的解决方案，但这是我迄今为止想到的：

public abstract class Person
{
    public String Name { get; set; }

    public override Boolean Equals(Object other)
    {
        var otherPerson = other as Person;

        if (otherPerson == null)
            return false;

        return Name.Equals(otherPerson.Name, StringComparison.OrdinalIgnoreCase);
    }
}

public class Employee : Person
{
    public DateTime? TerminationDate { get; set; }
}

public class Customer : Person
{
    ...
}


public class People
{
    private IEnumerable<Customer> Customers;
    private IEnumerable<Employee> Employees;

    public IEnumerable<Person> GetCurrentPeople()
    {
        // Find all customers that are not employees
        var onlyCustomers = Customers.Except(Employees);

        // We only want employees that have not been terminated
        var currentEmployees = Employees.Where(e => e.TerminationDate == null);

        // Find all customers that are also employees
        var customerAndEmployees = currentEmployees.Intersect(Customers);

        // Now deal with employees that are not customers
        var onlyEmployees = currentEmployees.Except(Customers);

        // Join the lists together
        var mergedRules = onlyCustomers.Concat(onlyEmployees).Concat(customerAndEmployees);

        return mergedRules;
    }
}