有没有一种简单的方法来展平一组对象，同时制作一个不同的列的数组？

Question

我有一个类似的对象数组：

 class StateVisitor
 {
     string FirstName { get; set; }
     string LastName { get; set; }
     string StateViseted { get; set; }
 }
    
 StateVisitor[] StateVisitors = {
     new() { FirstName = "Bob", LastName = "Smith", StateViseted = "AL" },
     new() { FirstName = "Bob", LastName = "Smith", StateViseted = "AK" },
     new() { FirstName = "Bob", LastName = "Jones", StateViseted = "AL" },
     new() { FirstName = "Sam", LastName = "Smith", StateViseted = "UT" }
  }

我想做这样的事情：

 class VisitorsWithCombinedStates {
    string FirstName { get; set; }
    string LastName { get; set; }
    string[] StatesVisetedArray { get; set; }
}

 VisitorsWithCombinedStates[] visitorsWithCombinedStates = StateVisitors... /* Linq magic? */

 visitorsWithCombinedStates.ForEach(v 
     => Console.WriteLine($"{v.FirstName} {v.LastName} visited {string.Join(", ",v.StatesVisitedArray)}"));

        // "Bob Smith visited AL, AK"
        // "Bob Jones visited AL"
        // "Sam Smith visited UT"

有没有一种简单的方法，在 C#（可能使用 LINQ）中将第一个数组展平为第二个数组，在其中创建访问状态的数组？

Answer 1

您想通过名字和姓氏的组合对您的项目进行分组，并将分组结果投影为仅访问过的 state

var groups = stateVisitors.GroupBy(sv => new
    {
        sv.FirstName,
        sv.LastName,
    },
    sv => sv.StateVisited );

Output：

foreach(var g in groups)
{
    // g.Key.FirstName
    // g.Key.LastName
    // g is IEnumerable<string> of visited states
}

Answer 2

一个例子，填写您的VisitorWithCombinedStates class：

VisitorsWithCombinedStates[] visitorsWithCombinedStates = StateVisitors.GroupBy(x => new { x.FirstName, x.LastName},x => x.StateViseted)
.Select(x => new VisitorsWithCombinedStates { FirstName = x.Key.FirstName, LastName = x.Key.LastName, StatesVisetedArray = x.ToArray() }).ToArray();

Answer 3

我认为您正在寻找GroupBy然后将组投影到您的新 class 中：

var visitorsWithCombinedStates = StateVisitors.GroupBy(sv => new { sv.FirstName, sv.LastName }, sv => sv.StateVisited)
                                              .Select(svg => new VisitorsWithCombinedStates {
                                                  FirstName = svg.Key.FirstName,
                                                  LastName = svg.Key.LastName,
                                                  StatesVisitedArray = svg.ToArray()
                                              })
                                              .ToArray();

注意：更正了visited的拼写