I have a problem which I've simplified down and have been scratching my head at. If I have a list of students and I want to use LINQ to produce a group of students by Age, Grade, and LastName so I can traverse them with a nested foreach loop how would I go about this. Here is some code:
class Student
{
public int Grade;
public int Age;
public string LastName;
}
public void SomeMethod()
{
Student student1 = new Student() { Age = 10, Grade = 100, LastName = "Smith"};
Student student2 = new Student() { Age = 10, Grade = 90, LastName = "Jones" };
Student student3 = new Student() { Age = 10, Grade = 50, LastName = "Bob" };
Student student4 = new Student() { Age = 10, Grade = 100, LastName = "Smith" };
Student student5 = new Student() { Age = 11, Grade = 10, LastName = "Bob" };
Student student6 = new Student() { Age = 11, Grade = 30, LastName = "Jones" };
Student student7 = new Student() { Age = 13, Grade = 90, LastName = "Bob" };
Student student8 = new Student() { Age = 13, Grade = 90, LastName = "Smithy" };
Student student9 = new Student() { Age = 15, Grade = 100, LastName = "Smith" };
Student student10 = new Student() { Age = 15, Grade = 0, LastName = "Smith" };
List<Student> studentList = new List<Student>()
{
student1,student2,student3,student4,student5,student6,student7,student8,student9,student10
};
var studentGroups = from student in studentList
group student by student.Age into studentAgeGroup
from studentAgeGradeGroup in
(
from student in studentAgeGroup
group student by student.Grade
)
group studentAgeGradeGroup by studentAgeGroup.Key;
foreach (var ageGroup in studentGroups)
{
foreach (var gradeGroup in ageGroup)
{
foreach (var innerGroupElement in gradeGroup)
{
// At this point they are grouped by age and grade but I would also like them to be grouped by LastName
}
}
}
}
How about?
var studentGroups = from student in studentList
group student by new {student.Age, student.Grade, student.LastName};
and looping through each element in studentGroups, you can access Age by sg.Key.Age and so on.
so I can traverse them with a nested foreach loop how would I go about this.
Like this:
var studentGroups =
from student in studentList
group student by new {student.Age, student.Grade, student.LastName} into g2
group g2 by new {g2.Key.Age, g2.Key.Grade} into g1
group g1 by g1.Key.Age
foreach(var group0 in studentGroups)
{
int age = group0.Key;
foreach(var group1 in group0)
{
int grade = group1.Key.Grade
foreach(var group2 in group1)
{
string lastName = group2.Key.LastName
foreach(Student s in group2)
{
//...
}
}
}
}
Why not group them straight away?
var studentGroups = from student in studentList
group student by new { student.Age, student.Grade, student.LastName }
into studentAgeGroup
select studentAgeGroup;
Related
I've created a list of courses that students are enrolled in. However, I can't figure out how to access the objects from the list in the Main. Below, I've tried to get the Student-Id and pull the information from there, but it isn't working. I'm new to coding please help
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;
namespace Jvstt_College
{
class Admin
{
##
## Dictionary<int, Student> studentList = new Dictionary<int, Student>();
Dictionary<int, Professor> professorList = new Dictionary<int, Professor>();
List<Course> courseList = new List<Course>();
Dictionary<int, Student> studentCourses = new Dictionary<int, Student>();
public Dictionary<int, Student> StudentList()
{
var Student1 = new Student() { FirstName = "Tom", LastName = " Jones", Password = "Test", EnrollmentId = 111111};
var Student2 = new Student() { FirstName = "Mark", LastName = " Thomas", Password = "Grace", EnrollmentId = 101203 };
var Student3 = new Student() { FirstName = "Jake", LastName = " Riley", Password = "SavedbyChrist1", EnrollmentId = 568903 };
var Student4 = new Student() { FirstName = "Olivia", LastName = " Beckam", Password = "GodisGood", EnrollmentId = 951357 };
var Student5 = new Student() { FirstName = "Myrai", LastName = " Bailey", Password = "ChildofGod", EnrollmentId = 741369 };
var Student6 = new Student() { FirstName = "Majea", LastName = " Bailey", Password = "CoastLand", EnrollmentId = 852146 };
studentList.Add(111111, Student1);
studentList.Add(101203, Student2);
studentList.Add(568903, Student3);
studentList.Add(951357, Student4);
studentList.Add(741369, Student5);
studentList.Add(852146, Student6);
return studentList;
}
public Dictionary<int, Professor> ProfessorList()
{
professorList.Add(654321, new Professor { FirstName = "Grace", LastName = "Riley", Password = "Gracey1983", EnrollmentId = 654321 });
enter code here professorList.Add(852963, new Professor { FirstName = "Liam", LastName = "Beckam", Password = "Password", EnrollmentId = `enter code here`852963 });
professorList.Add(359861, new Professor { FirstName = "Martha", LastName = "Hart", Password = "QwertYy00", EnrollmentId = 359861 });
professorList.Add(612832, new Professor { FirstName = "George", LastName = "Washington", Password = "Kid$nExtD00r", EnrollmentId = 612832 });
return professorList;
}
public List<Course> CourseList()
{
var Accounts = new Course() { CourseID = 101, CourseName = " Accounts " };
var Bio_Psychology = new Course() { CourseID = 102, CourseName = " Bio_Psychology " };
var Business = new Course() { CourseID = 103, CourseName = " Business " };
var Chemistry = new Course() { CourseID = 104, CourseName = " Chemistry " };
var CSWDCA = new Course() { CourseID = 105, CourseName = " Computer Science/Web Design/Cybersecurity Accounts" };
var Psychology = new Course() { CourseID = 106, CourseName = " Psychology " };
var Statistics = new Course() { CourseID = 107, CourseName = " Statistics " };
var Advance_Math = new Course() { CourseID = 108, CourseName = "Advance Math" };
courseList.Add(Accounts);
courseList.Add(Bio_Psychology);
courseList.Add(Business);
courseList.Add(Chemistry);
courseList.Add(CSWDCA);
courseList.Add(Psychology);
courseList.Add(Statistics);
courseList.Add(Advance_Math);
return courseList;
}
public Dictionary<int, Student> StudentEnrollments()
{
var Student1 = studentList[111111];
{
if(Student1.Courses == null)
{
Student1.Courses = new List<Course>();
Student1.Courses?.Add(courseList[0]);
Student1.Courses?.Add(courseList[2]);
Student1.Courses?.Add(courseList[4]);
}
}
var Student2 = studentList[101203];
{
if(Student2.Courses == null)
{
Student2.Courses = new List<Course>();
Student2.Courses?.Add(courseList[1]);
Student2.Courses?.Add(courseList[4]);
Student2.Courses?.Add(courseList[5]);
Student2.Courses?.Add(courseList[6]);
Student2.Courses?.Add(courseList[7]);
}
}
var Student3 = studentList[568903];
{
if (Student3.Courses == null)
{
Student3.Courses = new List<Course>();
Student3.Courses?.Add(courseList[1]);
Student3.Courses?.Add(courseList[4]);
}
}
var Student4 = studentList[951357];
{
if (Student4.Courses == null)
{
Student4.Courses = new List<Course>();
Student4.Courses?.Add(courseList[1]);
Student4.Courses?.Add(courseList[5]);
Student4.Courses?.Add(courseList[7]);
}
}
var Student5 = studentList[741369];
{
if (Student5.Courses == null)
{
Student5.Courses = new List<Course>();
Student5.Courses?.Add(courseList[0]);
Student5.Courses?.Add(courseList[2]);
Student5.Courses?.Add(courseList[3]);
Student5.Courses?.Add(courseList[6]);
Student5.Courses?.Add(courseList[7]);
}
}
var Student6 = studentList[852146];
{
if (Student6.Courses == null)
{
Student6.Courses = new List<Course>();
Student6.Courses?.Add(courseList[0]);
Student6.Courses?.Add(courseList[1]);
Student6.Courses?.Add(courseList[2]);
Student6.Courses?.Add(courseList[3]);
Student6.Courses?.Add(courseList[4]);
Student6.Courses?.Add(courseList[5]);
Student6.Courses?.Add(courseList[6]);
}
}
studentCourses.Add(111111,Student1);
studentCourses.Add(101203,Student2);
studentCourses.Add(568903,Student3);
studentCourses.Add(951357,Student4);
studentCourses.Add(741369,Student5);
studentCourses.Add(852146,Student6);
return studentCourses;
}
}
}
}
First, let's declare the Professor, Student and Course classes. Since Professor and Student have similar properties and since they both are persons, it makes sense to derive them both from an abstract Person class. An abstract class cannot be instantiated.
abstract class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string Password { get; set; }
public int EnrollmentId { get; set; }
}
class Professor : Person
{
}
class Student : Person
{
public List<Course> Courses { get; } = new List<Course>();
}
class Course
{
public int CourseID { get; set; }
public string CourseName { get; set; }
}
In class Student I created the Courses list as read-only property and initialized it with a property initializer. This saves you from having to do something like if (Student2.Courses == null) { Student2.Courses = new List<Course>(); ... } later.
You have several method initializing lists and dictionaries. Those should declare and create the collections they return. Otherwise, if the collections are declared in a surrounding scope, the return statement would not be required and the responsibilities would not be clear. Add also, a dictionary is not a list. Since these methods do rely on instance fields anymore, we make them static (and simplify them):
// In class Admin
private static Dictionary<int, Student> CreateStudents()
{
return new Dictionary<int, Student> {
{ 111111, new Student { FirstName = "Tom", LastName = " Jones", Password = "Test", EnrollmentId = 111111 } },
{ 101203, new Student { FirstName = "Mark", LastName = " Thomas", Password = "Grace", EnrollmentId = 101203 } },
{ 568903, new Student { FirstName = "Jake", LastName = " Riley", Password = "SavedbyChrist1", EnrollmentId = 568903 } },
{ 951357, new Student { FirstName = "Olivia", LastName = " Beckam", Password = "GodisGood", EnrollmentId = 951357 } },
{ 741369, new Student { FirstName = "Myrai", LastName = " Bailey", Password = "ChildofGod", EnrollmentId = 741369 } },
{ 852146, new Student { FirstName = "Majea", LastName = " Bailey", Password = "CoastLand", EnrollmentId = 852146 } }
};
}
private static Dictionary<int, Professor> CreateProfessors()
{
return new Dictionary<int, Professor> {
{ 654321, new Professor { FirstName = "Grace", LastName = "Riley", Password = "Gracey1983", EnrollmentId = 654321 } },
{ 852963, new Professor { FirstName = "Liam", LastName = "Beckam", Password = "Password", EnrollmentId = 852963 } },
{ 359861, new Professor { FirstName = "Martha", LastName = "Hart", Password = "QwertYy00", EnrollmentId = 359861 } },
{ 612832, new Professor { FirstName = "George", LastName = "Washington", Password = "Kid$nExtD00r", EnrollmentId = 612832 } }
};
}
private static List<Course> CreateCourses()
{
return new List<Course> {
new Course { CourseID = 101, CourseName = "Accounts" },
new Course { CourseID = 102, CourseName = "Bio_Psychology" },
new Course { CourseID = 103, CourseName = "Business" },
new Course { CourseID = 104, CourseName = "Chemistry" },
new Course { CourseID = 105, CourseName = "Computer Science/Web Design/Cybersecurity Accounts" },
new Course { CourseID = 106, CourseName = "Psychology" },
new Course { CourseID = 107, CourseName = "Statistics" },
new Course { CourseID = 108, CourseName = "Advance Math" }
};
}
Now, we can declare and initialize the collections like this:
class Admin
{
public readonly Dictionary<int, Student> students = CreateStudents();
public readonly Dictionary<int, Professor> professors = CreateProfessors();
public readonly List<Course> courses = CreateCourses();
...
}
I made them read-only. This only means that we cannot assign it another collection later. The collections themselves are still read/write.
We do not need another collection studentCourses, we can directly add the courses to the students in our existing students dictionary.
If we declare an instance method EnrollStudents in class Admin, then it can access the fields of this class.
public void EnrollStudents()
{
Student student = students[111111];
student.Courses.Add(courses[0]);
student.Courses.Add(courses[2]);
student.Courses.Add(courses[4]);
student = students[101203]; // It is okay to reuse the student variable
student.Courses.Add(courses[1]);
student.Courses.Add(courses[4]);
student.Courses.Add(courses[5]);
student.Courses.Add(courses[6]);
student.Courses.Add(courses[7]);
student = students[568903];
student.Courses.Add(courses[1]);
student.Courses.Add(courses[4]);
student = students[951357];
student.Courses.Add(courses[1]);
student.Courses.Add(courses[5]);
student.Courses.Add(courses[7]);
student = students[741369];
student.Courses.Add(courses[0]);
student.Courses.Add(courses[2]);
student.Courses.Add(courses[3]);
student.Courses.Add(courses[6]);
student.Courses.Add(courses[7]);
student = students[852146];
student.Courses.Add(courses[0]);
student.Courses.Add(courses[1]);
student.Courses.Add(courses[2]);
student.Courses.Add(courses[3]);
student.Courses.Add(courses[4]);
student.Courses.Add(courses[5]);
student.Courses.Add(courses[6]);
}
Note that we do not have to return anything. Since classes are reference types, all the students in the original students dictionary have now been updated with courses. Of course we must call this method somewhere (probably in Main).
But we can simplify this method with a new helper method, because we have a lot of repetitions we can avoid:
private void AddStudentCourses(Student student, params int[] courseIndexes)
{
foreach (int index in courseIndexes) {
student.Courses.Add(courses[index]);
}
}
public void EnrollStudents()
{
AddStudentCourses(students[111111], 0, 2, 4);
AddStudentCourses(students[101203], 1, 4, 5, 6, 7);
AddStudentCourses(students[568903], 1, 4);
AddStudentCourses(students[951357], 1, 5, 7);
AddStudentCourses(students[741369], 0, 2, 3, 6, 7);
AddStudentCourses(students[852146], 0, 1, 2, 3, 4, 5, 6);
}
Test:
var admin = new Admin();
admin.EnrollStudents();
var orderedStudents = admin.students.Values
.OrderBy(s => s.LastName)
.ThenBy(s => s.FirstName);
foreach (var student in orderedStudents) {
Console.WriteLine($"{student.LastName} {student.FirstName} ({student.EnrollmentId})");
IOrderedEnumerable<Course> orderedCourses = student.Courses.OrderBy(c => c.CourseName);
foreach (var course in orderedCourses) {
Console.WriteLine($" {course.CourseName} ({course.CourseID})");
}
Console.WriteLine();
}
Prints
Bailey Majea (852146)
Accounts (101)
Bio_Psychology (102)
Business (103)
Chemistry (104)
Computer Science/Web Design/Cybersecurity Accounts (105)
Psychology (106)
Statistics (107)
Bailey Myrai (741369)
Accounts (101)
Advance Math (108)
Business (103)
Chemistry (104)
Statistics (107)
Beckam Olivia (951357)
Advance Math (108)
Bio_Psychology (102)
Psychology (106)
Jones Tom (111111)
Accounts (101)
Business (103)
Computer Science/Web Design/Cybersecurity Accounts (105)
Riley Jake (568903)
Bio_Psychology (102)
Computer Science/Web Design/Cybersecurity Accounts (105)
Thomas Mark (101203)
Advance Math (108)
Bio_Psychology (102)
Computer Science/Web Design/Cybersecurity Accounts (105)
Psychology (106)
Statistics (107)
Join the two collections and calculate the total score of each student by subject.
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; }
}
public class StudentScoress
{
public static void Main(string[] args)
{
var totalscore = from s in Student
join ss in StudentScore
on s.Id equals ss.StudentId
group ss by ss.Subject into sss
select new { sss.Name, sss.Subject, sss.Points };
foreach (var ts in totalscore)
{
Console.WriteLine("{0}" + " " + "{1}" + " " + "{2}", ts.Name, ts.Subject, ts.Points);
}
}
IEnumerable<Student> student = new List<Student>()
{
new Student() {Id=1,Name="Sam",Age=16},
new Student() {Id=2,Name="Rick",Age=16},
new Student() {Id=3,Name="Warner",Age=17},
};
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 = 1, Subject = "Biology", Points = 32},
new StudentScore() { StudentId = 1, Subject = "Biology", Points = 27},
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 = 2, Subject = "Biology", Points = 42},
new StudentScore() { StudentId = 2, Subject = "Biology", Points = 67},
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},
new StudentScore() { StudentId = 3, Subject = "Biology", Points = 87},
new StudentScore() { StudentId = 3, Subject = "Biology", Points = 34}
};
}
I'm getting error in LINQ query that 'StudentScore' is a type, which is not valid in the given context.
What I'm missing here. Anyone help me out.
Demo on dotnet fiddle
You should replace Student model by student list.
You should replace StudentScore model by studentScores list.
You need to group by 2 fields new {s.Name, ss.Subject} to be able to get in selecting result.
Use Aggregate Operators like Sum function to get TotalScore or Average or Count, Max, Min etc.
var totalscore = from s in student
join ss in studentScores on s.Id equals ss.StudentId
group ss by new {s.Name, ss.Subject} into sss
select new { sss.Key.Name, sss.Key.Subject, TotalScore = sss.Sum(p => p.Points) };
foreach (var ts in totalscore)
{
Console.WriteLine("{0}" + " " + "{1}" + " " + "{2}", ts.Name, ts.Subject, ts.TotalScore);
}
Output
Sam Maths 86
Sam English 109
Sam Biology 59
Rick Maths 81
Rick English 123
Rick Biology 109
Warner Maths 125
Warner English 113
Warner Biology 121
I have class like this
public class Student
{
public int Id { get; set; }
public string Name { get; set; }
public string Gender { get; set; }
public GRADE Grade { get; set; }
public string Nationality { get; set; }
}
public enum GRADE
{
A = 0,
B = 1,
C = 2,
D = 3,
E = 4
}
var list = new List<Student>();
list.Add(new Student() { Id = 1, Name = "Prasad", Gender = "M", Nationality = "India", Grade = GRADE.A });
list.Add(new Student() { Id = 2, Name = "Raja", Gender = "M", Nationality = "India", Grade = GRADE.B });
list.Add(new Student() { Id = 3, Name = "Hindu", Gender = "F", Nationality = "India", Grade = GRADE.A });
list.Add(new Student() { Id = 4, Name = "Hamed", Gender = "M", Nationality = "India", Grade = GRADE.C });
list.Add(new Student() { Id = 5, Name = "Priya", Gender = "F", Nationality = "India", Grade = GRADE.D });
list.Add(new Student() { Id = 6, Name = "Meera", Gender = "F", Nationality = "India", Grade = GRADE.B });
I got the solution like this, For each expression i want to write bunch of code.. Sum,Avg,Count etc
Linq Expressions
//count
var c = (from x in list.GroupBy(k => k.Gender)
select new
{
category = x.Key,
Value = x.Count()
}).ToList();
//sum
var s = (from x in list.GroupBy(k => k.Gender)
select new
{
category = x.Key,
Value = x.Sum(k => (int)k.Grade)
}).ToList();
//avg
var a = (from x in list.GroupBy(k => k.Gender)
select new
{
category = x.Key,
Value = x.Average(k => (int)k.Grade)
}).ToList();
I am trying to make one function, based on the aggregate function; it should return the value, I tried I could not find it.
One issue you have is that all three aggregates do not have the same return type, also if you use a function then the return type would have to be object because you are returning an anonymous type.
The closest I could get to what I think you want was this;
Step 1: create a new type;
public class AggregateValue<T>
{
public string Category { get; set; }
public T Value { get; set; }
}
Step 2: Create a function that returns a collection of this type and accepts a Func as a parameter that will calculate your different aggregates;
IEnumerable<AggregateValue<T>> GetAggregateValues<T>(List<Student> students, Func<IEnumerable<Student>, T> aggregateFunction)
{
return (from x in students.GroupBy(k => k.Gender)
select new AggregateValue<T>
{
Category = x.Key,
Value = aggregateFunction(x)
}).ToList();
}
You can use it like this;
var list = new List<Student>();
list.Add(new Student() { Id = 1, Name = "Prasad", Gender = "M", Nationality = "India", Grade = GRADE.A });
list.Add(new Student() { Id = 2, Name = "Raja", Gender = "M", Nationality = "India", Grade = GRADE.B });
list.Add(new Student() { Id = 3, Name = "Hindu", Gender = "F", Nationality = "India", Grade = GRADE.A });
list.Add(new Student() { Id = 4, Name = "Hamed", Gender = "M", Nationality = "India", Grade = GRADE.C });
list.Add(new Student() { Id = 5, Name = "Priya", Gender = "F", Nationality = "India", Grade = GRADE.D });
list.Add(new Student() { Id = 6, Name = "Meera", Gender = "F", Nationality = "India", Grade = GRADE.B });
var sumGrades = new Func<IEnumerable<Student>, int>(p => p.Sum(l => (int)l.Grade));
var aveGrades = new Func<IEnumerable<Student>, double>(p => p.Average(k => (int)k.Grade));
var count = new Func<IEnumerable<Student>, int>(p => p.Count());
var c = GetAggregateValues(list, count);
var s = GetAggregateValues(list, sumGrades);
var a = GetAggregateValues(list, aveGrades);
You can combine all your aggregations in one statement:
var result = (from x in list.GroupBy(k => k.Gender)
select new
{
category = x.Key,
Count = x.Count(),
Sum = x.Sum(k => (int)k.Grade),
Average = x.Average(k => (int)k.Grade)
}).ToList();
How to print out all the persons and their pets, using Linq. I only want to print out persons who have pets.
Prefer result be like:
Kate Bed:
Rex
Sally
My not working solution is here:
class Program
{
static void Main(string[] args)
{
result();
}
static void result() {
var list = StaticGenator.getPersons().Where(x => x.Pets != null);
foreach (var person in list)
{
Console.WriteLine(person.Firstname + " " + person.Lastname + ":");
foreach(var pet in list){
Console.WriteLine(" " + pet.Pets);
}
}
}
What i get is:
Kate Bed:
system.collection.generic.list'1[MainLibrary.Pet]
system.collection.generic.list'1[MainLibrary.Pet]
Here is the code to understand what I am asking:
Data is held here:
public static class StaticGenator
{
public static List<Person> getPersons()
{
List<Person> persons = new List<Person>();
persons.Add(new Person() { Firstname = "Sam", Lastname = "Car", BirthDate = new DateTime(2001, 01, 01), PersonId = 1, Sex = Sex.Man });
persons.Add(new Person() { Firstname = "Kate", Lastname = "Bed", BirthDate = new DateTime(1995, 11, 11), PersonId = 2, Sex = Sex.Woman, Pets = new List<Pet>() { new Pet { Firstname = "Rex", BirthDate = new DateTime(2007, 1, 1), Sex = Sex.Man, PetId = 1 }, new Pet { Firstname = "Sally", BirthDate = new DateTime(2004, 2, 1), Sex = Sex.Woman, PetId = 2 } } });
return persons;
}
}
Person Class:
public class Person
{
public int PersonId { get; set; }
public string Firstname { get; set; }
public string Lastname { get; set; }
public DateTime BirthDate { get; set; }
public Sex Sex{ get; set; }
public int Age {
get
{
var age= DateTime.Now.Year - BirthDate.Year;
if (DateTime.Now.Day >= BirthDate.Day && DateTime.Now.Month >= BirthDate.Month)
return age;
else
return age- 1;
}
}
public List<Pet> Pets { get; set; }
}
Pet Class:
public class Pet
{
public int PetId { get; set; }
public String Firstname { get; set; }
public Sex Sex { get; set; }
public DateTime BirthDate { get; set; }
public int Age { get; set; }
}
Sex enum:
public enum Sex{
Man,
Woman
}
foreach (var person in list)
{
Console.WriteLine(person.Firstname + " " + person.Lastname + ":");
foreach(var pet in person.Pets) // iterate over Pets of person
{
Console.WriteLine(" " + pet.Firstname); // write pet's name
}
}
Keep in mind - you can have problem if somebody will add null pet to pets collection or if there is empty pets list. So, probably correct query to get persons with pets is:
var peopleWithPets = from p in StaticGenator.getPersons()
where p.Pets != null &&
p.Pets.Any() &&
p.Pets.All(x => x != null)
select p;
Also use string formatting:
foreach (var person in peopleWithPets)
{
Console.WriteLine("{0} {1}:", person.Firstname, person.Lastname);
foreach(var pet in person.Pets)
Console.WriteLine("\t{0}", pet.Firstname);
}
Also I suggest you to follow Capitalization Styles recommended by MicroSoft.
foreach(var pet in list)
{
Console.WriteLine(" " + pet.Pets);
}
Should be:
foreach(var pet in person.Pets)
{
Console.WriteLine(" " + pet.FirstName);
}
You have to iterate over the pet collection of the current user that is being iterated.
Suppose you have some list (you mentioned above) with your datastructure
List<Person> persons = new List<Person>();
persons.Add(new Person() { Firstname = "Sam", Lastname = "Car", BirthDate = new DateTime(2001, 01, 01), PersonId = 1, Sex = Sex.Man });
persons.Add(new Person() { Firstname = "Kate", Lastname = "Bed", BirthDate = new DateTime(1995, 11, 11), PersonId = 2, Sex = Sex.Woman, Pets = new List<Pet>() { new Pet { Firstname = "Rex", BirthDate = new DateTime(2007, 1, 1), Sex = Sex.Man, PetId = 1 }, new Pet { Firstname = "Sally", BirthDate = new DateTime(2004, 2, 1), Sex = Sex.Woman, PetId = 2 } } });
You can very easily filter as well as write to console with these 4 lines of code
persons.Where(p => p.Pets != null && p.Pets.Any()).ToList().ForEach(p =>
{
Console.WriteLine(p.Firstname + " " + p.Lastname + "\n");
p.Pets.ForEach(pt => Console.WriteLine(pt.Firstname));
});
var output = String.Join("\n", persons.Select(person => $"{person.Firstname} {person.Lastname}"));
Output:
Sam Car
Kate Bed
I'm trying to write a program that shows duplicate records to the user to correct the data or remove the duplicate rows. It works, but I had to put a Where clause in my lambda expression to get this working. How can I remove this useless clause?
Where(d => d.Id > 0) at line 22.
public class Person
{
public int Id { get; set; }
public string Name { get; set; }
public int Age { get; set; }
}
public class Program
{
static void Main(string[] args)
{
List<Person> dt = new List<Person>();
dt.Add(new Person() { Id = 1, Name = "MICHAEL JACKSON", Age = 50 });
dt.Add(new Person() { Id = 2, Name = "MICHAEL JACKSON", Age = 51 });
dt.Add(new Person() { Id = 3, Name = "JOHN LENNON", Age = 40 });
dt.Add(new Person() { Id = 4, Name = "JOHN LENNON", Age = 41 });
dt.Add(new Person() { Id = 5, Name = "ELVIS PRESLEY", Age = 42 });
var duplicates = dt.AsEnumerable().GroupBy(r => r.Name).Where(gr => gr.Count() > 1).ToList();
if (duplicates.Any())
{
var query = duplicates.SelectMany(c => c.Where(d => d.Id > 0)).AsQueryable();
foreach (var item in query)
Console.WriteLine(String.Format("{0} - {1}", item.Name, item.Age));
}
else
Console.WriteLine("No records duplicates.");
Console.ReadLine();
}
}
This is just sample code, my code does a lot of other checks, but if somebody knows how to remove this clause it will be very helpful to me. I think it could impact performance.
this here also works:
List<Person> dt = new List<Person>();
dt.Add(new Person() { Id = 1, Name = "MICHAEL JACKSON", Age = 50 });
dt.Add(new Person() { Id = 2, Name = "MICHAEL JACKSON", Age = 51 });
dt.Add(new Person() { Id = 3, Name = "JOHN LENNON", Age = 40 });
dt.Add(new Person() { Id = 4, Name = "JOHN LENNON", Age = 41 });
dt.Add(new Person() { Id = 5, Name = "ELVIS PRESLEY", Age = 42 });
var duplicates = dt.GroupBy(r => r.Name).Where(gr => gr.Count() > 1).ToList();
if (duplicates.Any())
{
foreach (var item in duplicates)
Console.WriteLine(String.Format("{0} - {1}", item.Key, string.Join(",", item.Select(p => p.Age))));
}
else
Console.WriteLine("No records duplicates.");
Console.ReadLine();
This works for me.
var query = duplicates.SelectMany(c => c).AsQueryable();
thats becouse duplicates is the grouped by object. try this if you only want to show the name:
var query = duplicates.Select(c => c.Key);
foreach (var item in query)
Console.WriteLine(String.Format("{0}", item));
try this if you want to show repeated ages:
var query = duplicates.SelectMany(i => i);
foreach (var item in query)
Console.WriteLine(String.Format("{0} - {1}", item.Name, item.Age));