LINQ 学习路程 -- 查询操作 Average Count Max Sum

IList<int> intList = new List<int>>() { 10, 20, 30 };

var avg = intList.Average();

Console.WriteLine("Average: {0}", avg);

IList<Student> studentList = new List<Student>>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 13} ,
        new Student() { StudentID = 2, StudentName = "Moin",  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 = 15 } 
    };

var avgAge = studentList.Average(s => s.Age);

Console.WriteLine("Average Age of Student: {0}", avgAge);

var totalAge = (from s in studentList
                select s.age).Count(); 

int Count<TSource>();

int Count<TSource>(Func<TSource, bool> predicate);

IList<Student> studentList = new List<Student>>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 13} ,
        new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
        new Student() { StudentID = 4, StudentName = "Ram" , Age = 20} ,
        new Student() { StudentID = 5, StudentName = "Mathew" , Age = 15 } 
    };

var numOfStudents = studentList.Count();

Console.WriteLine("Number of Students: {0}", numOfStudents);

// Student collection
IList<Student> studentList = new List<Student>>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 13} ,
        new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
        new Student() { StudentID = 4, StudentName = "Ram" , Age = 20} ,
        new Student() { StudentID = 5, StudentName = "Mathew" , Age = 15 } 
    };

var numOfStudents = studentList.Count(s => s.Age >= 18);

Console.WriteLine("Number of Students: {0}", numOfStudents);

IList<int> intList = new List<int>() { 10, 21, 30, 45, 50, 87 };

var largest = intList.Max();

Console.WriteLine("Largest Element: {0}", largest);

var largestEvenElements = intList.Max(i => {
                                    if(i%2 == 0)
                                        return i;
            
                                    return 0;
                                });

Console.WriteLine("Largest Even Element: {0}", largestEvenElements );

IList<Student> studentList = new List<Student>>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 13} ,
        new Student() { StudentID = 2, StudentName = "Moin",  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 = 15 } 
    };

var oldest = studentList.Max(s => s.Age);

Console.WriteLine("Oldest Student Age: {0}", oldest);

public class Student : IComparable<Student> 
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
    public int StandardID { get; set; }

    public int CompareTo(Student other)
    {
        if (this.StudentName.Length >= other.StudentName.Length)
            return 1;

        return 0;
    }
}

class Program
{
    static void Main(string[] args)
    {
        // Student collection
        IList<Student> studentList = new List<Student>>() { 
                new Student() { StudentID = 1, StudentName = "John", Age = 13} ,
                new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,
                new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
                new Student() { StudentID = 4, StudentName = "Ram" , Age = 20} ,
                new Student() { StudentID = 5, StudentName = "Steve" , Age = 15 } 
            };

        var studentWithLongName = studentList.Max();

        Console.WriteLine("Student ID: {0}, Student Name: {1}", 
                                        .StudentID, studentWithLongName.StudentName)
    }
}

IList<int> intList = new List<int>() { 10, 21, 30, 45, 50, 87 };

var total = intList.Sum();

Console.WriteLine("Sum: {0}", total);

var sumOfEvenElements = intList.Sum(i => {
                                    if(i%2 == 0)
                                        return i;
            
                                    return 0;
                                });

Console.WriteLine("Sum of Even Elements: {0}", sumOfEvenElements );

IList<Student> studentList = new List<Student>>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 13} ,
        new Student() { StudentID = 2, StudentName = "Moin",  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 = 15 } 
    };

var sumOfAge = studentList.Sum(s => s.Age);

Console.WriteLine("Sum of all student's age: {0}", sumOfAge);
        
var numOfAdults = studentList.Sum(s => {
            
    if(s.Age >= 18)
        return 1;
    else
        return 0;
});
 
Console.WriteLine("Total Adult Students: {0}", numOfAdults);