c# - 究竟SelectMany()是做什么用的？

没有输入和输出，很难解释这一点。我制作了一个简单的Car示例，以避免不必要的项目细节。

我有这个清单：

List<car> cars = new List<car>()
{
    new car() { carname = "bmw", carwheels = new List<int>() { 1, 2, 3, 4 } },
    new car() { carname = "cadillac", carwheels = new List<int>() { 1, 2, 3, 4 } },
    new car() { carname = "mustang", carwheels = new List<int>() { 1, 2, 3, 4 } }
};

我想用扩展类输出它：

{
    { carname = "bmw", carwheel = 1 },
    { carname = "bmw", carwheel = 2 },
    { carname = "bmw", carwheel = 3 },
    { carname = "bmw", carwheel = 4 },
    { carname = "cadillac", carwheel = 1 },
    { carname = "cadillac", carwheel = 2 },
    { carname = "cadillac", carwheel = 3 },
    { carname = "cadillac", carwheel = 4 },
    { carname = "mustang", carwheel = 1 },
    { carname = "mustang", carwheel = 2 },
    { carname = "mustang", carwheel = 3 },
    { carname = "mustang", carwheel = 4 }
}

有没有一种方法可以通过IEnumerable扩展方法进行投影？类似于SelectMany（）的行为。

最佳答案

它不是SelectMany()的反义词，而是SelectMany()的确切含义。您可以这样实现：

var result = cars.SelectMany(c =>
            c.carwheels.Select(w => new
            {
                carname = c.carname,
                carwheel = w
            })).ToList();

内部的Select将每辆汽车的车轮投影到一个新的对象（在我的代码中，带有指定属性的匿名类型）。外部SelectMany()将这些序列拼合为一个列表。