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c# - 使用字典> 在 C# 的列表中查找最常见的出现

问题描述

假设我的 C# 代码定义如下，我想向控制台返回一个输出，显示列表或汽车中最常见的燃料类型。

// set delegates defining rules as a function that takes list of cars and returns an int
Func<List<Car>, int> CountElectric = (cars) => cars
    .GroupBy(c => c.IsElectric == true).Count(); // count electric cars

Func<List<Car>, int> CountGassoline = (cars) => cars
    .GroupBy(c => c.FuelType == FuelTypes.Gassoline).Count(); // count cars using gassoline

Func<List<Car>, int> CountDiesel = (cars) => cars
    .GroupBy(c => c.FuelType == FuelTypes.Diesel).Count(); // Count cars using diesel

// Add rules to dictionary of (Key=CarType, Value=Func<List<Car>, bool>
CarsRules = new Dictionary<CarType, Func<List<Car>, int>>()
{
    {FueldType.Electric, CountElectric},
    {FueldType.Diesel,CountDiesel},
    {FueldType.Gassoline, CountGassoline}
};

// Create List of Cars and add some cars
List<Car> cars = new List<Car>();

cars.Add(new Car() 
{Id = Guid, Name = "Tesla", IsElectric = true, FuelType = FuelTypes.Electric};

cars.Add(new Car() 
{Id = Guid, Name = "VW", IsElectric = false, FuelType = FuelTypes.Gassoline};

cars.Add(new Car() 
{Id = Guid, Name = "Toyota", IsElectric = false, FuelType = FuelTypes.Gassoline};

cars.Add(new Car() 
{Id = Guid, Name = "Volvo", IsElectric = false, FuelType = FuelTypes.Diesel};

在上面的汽车列表中，汽油是最常见的。我怎么知道呢？IE 我想在控制台上显示只是“汽油”

如果我在上面的列表中打成平手，例如 2 辆使用汽油的汽车和 2 辆使用柴油的汽车，我将如何找到并退回两者？IE 我想在控制台上显示“汽油”和“柴油”

我很难理解这种结构，我想像下面这样用老式的方式来做，但我很清楚应该有更优雅的方式来使用 Func 代表

public List<string> GetMostUsedFuelTypes(List<Car> cars)
{
    List<string> winners = new List<string>();

    int CountElectric = 0;
    int CountGassoline = 0;
    int CountDiesel = 0;

    foreach(var car in cars)
    {
        // Count and return fuel type that occurs most, if a tye, return the highest counts
    }

    return winners;
}

标签： c#dictionarylambdadelegatesfunc

解决方案

var mostCommonFuelType =
    cars
        .GroupBy(car => car.FuelType)
        .OrderBy(carsByFuelType => carsByFuelType.Count())
        .Select(carsByFuelType => carsByFuelType.Key
        .FirstOrDefault();

如果您需要自定义规则，只需让规则选择要在其分组中使用的键。除非它们不是互斥的，在这种情况下，您还需要使用 SelectMany 并返回键和值对。

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