C # Linq query help remove foreach loops by creating clean code

Question

Is there a way to remove for loops using linq to solve the problem i have

I want to get the subject and the amount of points for each student and each subject in this list:

IEnumerable<Student> students = new List<Student> {
    new Student() {Id = 1, Name = "John", Age = 13},
    new Student() {Id = 2, Name = "Mary", Age = 12},
    new Student() {Id = 3, Name = "Anne", Age = 14}
};

I have a second list containing all the ratings and information about the subject:

IEnumerable<StudentScore> studentScores = new List<StudentScore> {
    new StudentScore() {StudentId = 1, Subject = "Maths", Points = 54},
    new StudentScore() {StudentId = 1, Subject = "Maths", Points = 32},
    new StudentScore() {StudentId = 1, Subject = "English", Points = 55},
    new StudentScore() {StudentId = 1, Subject = "English", Points = 54},

    new StudentScore() {StudentId = 2, Subject = "Maths", Points = 44},
    new StudentScore() {StudentId = 2, Subject = "Maths", Points = 37},
    new StudentScore() {StudentId = 2, Subject = "English", Points = 59},
    new StudentScore() {StudentId = 2, Subject = "English", Points = 64},

    new StudentScore() {StudentId = 3, Subject = "Maths", Points = 53},
    new StudentScore() {StudentId = 3, Subject = "Maths", Points = 72},
    new StudentScore() {StudentId = 3, Subject = "English", Points = 54},
    new StudentScore() {StudentId = 3, Subject = "English", Points = 59},
};

This is the solution I came across:

foreach (var student in students)
{
    foreach (var studentScore in studentScores.Select(ss=>ss.Subject).Distinct())
    {
        Console.WriteLine("Name: " + student.Name + " Subject:" + studentScore + "Score: " + studentScores.Where(ss => ss.StudentId == student.Id)
                                                                               .Where(ss => ss.Subject == studentScore)
                                                                               .Sum(ss => ss.Points));
    }
}

Answer 1

Your solution has both a belt and suspenders - loops are foreachcombined with LINQ, where part of LINQ depends on the values ​​through which you enter the loop foreach.

, LINQ, , LINQ , . , , foreach, string.Format, .

:

var rows = students
    .Join(
        studentScores
    ,   st => st.Id
    ,   sc => sc.StudentId
    ,   (st, sc) => new { Student = st, Score = sc }
    )
    .GroupBy(p => new { p.Student.Id, p.Score.Subject })
    .Select(g => new {
        Name = g.First().Student.Name
    ,   Subj = g.Key.Subject
    ,   Points = g.Sum(p => p.Score.Points)
    })
    .ToList();

foreach :

foreach (var r in rows) {
    Console.WriteLine($"Name: {r.Name} Subject: {r.Subject} Score: {r.Score}");
}

Answer 2

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


namespace ConsoleApplication27
{
    class Program
    {

        static void Main(string[] args)
        {
            IEnumerable<Student> students = new List<Student> {
                new Student() {Id = 1, Name = "John", Age = 13},
                new Student() {Id = 2, Name = "Mary", Age = 12},
                new Student() {Id = 3, Name = "Anne", Age = 14}
            };
            IEnumerable<StudentScore> studentScores = new List<StudentScore> {
                new StudentScore() {StudentId = 1, Subject = "Maths", Points = 54},
                new StudentScore() {StudentId = 1, Subject = "Maths", Points = 32},
                new StudentScore() {StudentId = 1, Subject = "English", Points = 55},
                new StudentScore() {StudentId = 1, Subject = "English", Points = 54},

                new StudentScore() {StudentId = 2, Subject = "Maths", Points = 44},
                new StudentScore() {StudentId = 2, Subject = "Maths", Points = 37},
                new StudentScore() {StudentId = 2, Subject = "English", Points = 59},
                new StudentScore() {StudentId = 2, Subject = "English", Points = 64},

                new StudentScore() {StudentId = 3, Subject = "Maths", Points = 53},
                new StudentScore() {StudentId = 3, Subject = "Maths", Points = 72},
                new StudentScore() {StudentId = 3, Subject = "English", Points = 54},
                new StudentScore() {StudentId = 3, Subject = "English", Points = 59},
            };

            var groups = (from student in students
                          join studentScore in studentScores on student.Id equals studentScore.StudentId into st
                          select new { name = student.Name, scores = st })
                         .Select(x => x.scores.GroupBy(y => y.Subject).Select(z => new { name = x.name, subject = z.Key, totalPoints = z.Select(a => a.Points).Sum() }).ToList()).ToList();
            foreach(var group in groups)
            {
                foreach(var subject in group)
                {
                    Console.WriteLine("Student Name : '{0}', Subject : '{1}', Total Score : '{2}'", subject.name, subject.subject, subject.totalPoints);
                }
            }
        }
    }
    public class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
    }
    public class StudentScore
    {
        public int StudentId { get; set; }
        public string Subject { get; set; }
        public int Points { get; set; }
    }
}