LINQ 学习路程 -- 查询操作 Conversion Operators
Method | Description |
---|---|
AsEnumerable | Returns the input sequence as IEnumerable<t> |
AsQueryable | Converts IEnumerable to IQueryable, to simulate a remote query provider |
Cast | Coverts a non-generic collection to a generic collection (IEnumerable to IEnumerable<T>) |
OfType | Filters a collection based on a specified type |
ToArray | Converts a collection to an array |
ToDictionary | Puts elements into a Dictionary based on key selector function |
ToList | Converts collection to List |
ToLookup | Groups elements into an Lookup<TKey,TElement> |
class Program { static void ReportTypeProperties<T>(T obj) { Console.WriteLine("Compile-time type: {0}", typeof(T).Name); Console.WriteLine("Actual type: {0}", obj.GetType().Name); } static void Main(string[] args) { Student[] studentArray = { new Student() { StudentID = 1, StudentName = "John", Age = 18 } , new Student() { StudentID = 2, StudentName = "Steve", Age = 21 } , new Student() { StudentID = 3, StudentName = "Bill", Age = 25 } , new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } , new Student() { StudentID = 5, StudentName = "Ron" , Age = 31 } , }; ReportTypeProperties( studentArray); ReportTypeProperties(studentArray.AsEnumerable()); ReportTypeProperties(studentArray.AsQueryable()); } }
Cast
class Program
{
static void ReportTypeProperties<T>(T obj)
{
Console.WriteLine("Compile-time type: {0}", typeof(T).Name);
Console.WriteLine("Actual type: {0}", obj.GetType().Name);
}
static void Main(string[] args)
{
Student[] studentArray = {
new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
new Student() { StudentID = 2, StudentName = "Steve", Age = 21 } ,
new Student() { StudentID = 3, StudentName = "Bill", Age = 25 } ,
new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
new Student() { StudentID = 5, StudentName = "Ron" , Age = 31 } ,
};
ReportTypeProperties( studentArray);
ReportTypeProperties(studentArray.Cast<Student>());
}
}
IList<string> strList = new List<string>() { "One", "Two", "Three", "Four", "Three" }; string[] strArray = strList.ToArray<string>();// converts List to Array IList<string> list = strArray.ToList<string>(); // converts array into list
IList<Student> studentList = new List<Student>() {
new Student() { StudentID = 1, StudentName = "John", age = 18 } ,
new Student() { StudentID = 2, StudentName = "Steve", age = 21 } ,
new Student() { StudentID = 3, StudentName = "Bill", age = 18 } ,
new Student() { StudentID = 4, StudentName = "Ram" , age = 20 } ,
new Student() { StudentID = 5, StudentName = "Ron" , age = 21 }
};
//following converts list into dictionary where StudentId is a key
IDictionary<int, Student> studentDict =
studentList.ToDictionary<Student, int>(s => s.StudentID);
foreach(var key in studentDict.Keys)
Console.WriteLine("Key: {0}, Value: {1}",
key, (studentDict[key] as Student).StudentName);