C#.NET 利用ToDictionary(),GroupBy(),可以将List转化为Dictionary,主需要一行代码!
首先看一下需求,已知cars,等于:
List<Car> cars = new List<Car>(){ new Car(1,"audiA6","private"), new Car(2,"futon","merchant"), new Car(3,"feiren","bike"), new Car(4,"bukon","private"), new Car(5,"baoma","private"), new Car(6,"dayun","merchant") };
1)我想以id为键,值为Car转化为一个字典idCarDict,方法如下:
var idCarDict = cars.ToDictionary(car=>car.id);
这样保证能正确转化的前提为,id在列表中没有重复值。如果有重复的,会抛出向字典中添加重复值的异常。
2)我想以type为键,值car的List的typeDict,方法如下:
Dictionary<string, List<Car>> typeCarDict = cars.GroupBy(car => car.type).ToDictionary(r => r.Key, r => r.ToList());
分步解释:
第一步分组
cars.GroupBy(car=>car.type) //返回的结果类型为: //IEnumerable<IGroup<string,car>>; //其中string等于car.type,也就是分组的键
第二步将IEnumerable类型转化为字典,选取合适的键,
ToDictionary(r=>r.Key,r=>r.ToList());//r参数代表分组对象,r.Key便是car.type;//r.ToList()操作后将分组对象转化为List对象
这种转化代码简介,比以下foreach遍历得到以car.type的字典简洁许多:
var dict = new Dictionary<string,List<Car>>(); foreach(var car in cars) { if(dict.Contains(car.type)) dict[car.type].Add(car); else dict.Add(car.type,new List<Car>(){car}));}
C#.NET 利用ToDictionary(),GroupBy(),可以将List转化为Dictionary,主需要一行代码!
首先看一下需求,已知cars,等于:
List<Car> cars = new List<Car>(){ new Car(1,"audiA6","private"), new Car(2,"futon","merchant"), new Car(3,"feiren","bike"), new Car(4,"bukon","private"), new Car(5,"baoma","private"), new Car(6,"dayun","merchant") };
1)我想以id为键,值为Car转化为一个字典idCarDict,方法如下:
var idCarDict = cars.ToDictionary(car=>car.id);
这样保证能正确转化的前提为,id在列表中没有重复值。如果有重复的,会抛出向字典中添加重复值的异常。
2)我想以type为键,值car的List的typeDict,方法如下:
Dictionary<string, List<Car>> typeCarDict = cars.GroupBy(car => car.type).ToDictionary(r => r.Key, r => r.ToList());
分步解释:
第一步分组
cars.GroupBy(car=>car.type) //返回的结果类型为: //IEnumerable<IGroup<string,car>>; //其中string等于car.type,也就是分组的键
第二步将IEnumerable类型转化为字典,选取合适的键,
ToDictionary(r=>r.Key,r=>r.ToList());//r参数代表分组对象,r.Key便是car.type;//r.ToList()操作后将分组对象转化为List对象
这种转化代码简介,比以下foreach遍历得到以car.type的字典简洁许多:
var dict = new Dictionary<string,List<Car>>(); foreach(var car in cars) { if(dict.Contains(car.type)) dict[car.type].Add(car); else dict.Add(car.type,new List<Car>(){car})); }