有并没有一种简单的方法可以使一个对象数组变平，同时生成一个不同的列数组

Question

我有一个类似于以下的对象数组：

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"

在C#中(可能使用LINQ(，有没有一种简单的方法可以将第一个数组扁平化为第二个数组，在那里它可以生成一个访问状态的数组？

Answer 1

我认为您正在寻找GroupBy，然后将组投影到您的新类中：

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：已更正已访问的拼写

Answer 2

您希望按名字和姓氏的组合对项目进行分组，并将分组结果投影为访问状态的

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

输出：

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

Answer 3

例如，用CombinedStates类填充Visitors:

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();