Convert lambda expression into linq c#

Question

I have List of students and List of lecturers and I wrote code with double foreach statements.

Is there any way of simplifying this code using Lambda expressions?

public void GetLecturersWorkloadStatistics(List<Student> studentList, List<Lecturer> lecturerList)
{
    foreach (Lecturer lecturer in lecturerList)
    {
        foreach (Student student in studentList)
        {
            if (lecturer.ModuleName == student.ModuleName && lecturer.LastName == student.LecturerLastName &&
                lecturer.FirstName == student.LecturerFirstName)
            {
                lecturer.Credits = lecturer.Credits + lecturer.ModuleValueInCredits;
            }
        }
    }
}

are you asking how to translate this code into query syntax? — Ousmane D., May 21 '18 at 19:29
[It already **is** linq...](https://stackoverflow.com/questions/46070567/can-a-method-chain-be-called-linq/46070703#46070703) — Zohar Peled, May 21 '18 at 19:30
*= new List();* is useless. You are re-assigning it two lines below. — xanatos, May 21 '18 at 19:32
Not only is that code already linq, but if you meant you wanted it written using query syntax, query syntax uses lambdas as well. — Servy, May 21 '18 at 19:32
You also shouldn't call a variable `linkedList` when it's not a `LinkedList` (it's a `List`). — Servy, May 21 '18 at 19:32
@Servy They (the lambdas) are "hidden" in the query syntax :-) As we say in Italy, "Occhio non vede, cuore non duole" (Eye doesn't see, heart doesn't ache) — xanatos, May 21 '18 at 19:32
BTW, that code will blow up if `text` doesn't have a space in it...(`IndexOutOfRangeException`) — Rufus L, May 21 '18 at 19:33
And your condition is missing parenthesis to separate the `&&` and the `||`... — Zohar Peled, May 21 '18 at 19:36
@ja72 public string ModuleName { get; set; } public string LastName { get; set; } public string FirstName { get; set; } public string Group { get; set; } public string LecturerFirstName { get; set; } public string LecturerLastName { get; set; } public int Credits { get; set; } — last of us fan, May 21 '18 at 19:40
@JustGalgaldas - not in the comments!!! edit the question to add this information. — John Alexiou, May 21 '18 at 19:41

Rufus L · Answer 1 · 2018-05-21T20:06:27.417

I think the example you're trying doesn't work because it's returning an IEnumerable<Student> and your method is supposed to return a List<Student>;

You're also missing some parenthesis needed to group your && clauses together, so they're separated by the || operator.

One way to solve this would be to change the return type of your method to IEnumerable<Student>, and to add some parenthesis around your && clauses:

public IEnumerable<Student> GetStudentBySelectedLecturer(List<Student> linkedList,
    string text)
{
    var lecturerInformation = text.Split(' ');

    return from stud in linkedList
        where (stud.LecturerFirstName == lecturerInformation[0] &&
                stud.LecturerLastName == lecturerInformation[1]) ||
                (stud.LecturerFirstName == lecturerInformation[1] &&
                stud.LecturerLastName == lecturerInformation[0])
        select stud;
}

Another way would be to cast the return value to a List<Student>:

public List<Student> GetStudentBySelectedLecturer(List<Student> linkedList,
    string text)
{
    var lecturerInformation = text.Split(' ');

    return (from stud in linkedList
        where (stud.LecturerFirstName == lecturerInformation[0] &&
               stud.LecturerLastName == lecturerInformation[1]) ||
              (stud.LecturerFirstName == lecturerInformation[1] &&
               stud.LecturerLastName == lecturerInformation[0])
        select stud).ToList();
}

Of course there are still some potential problems, like if either linkedList or lecturer is null, or if there is no space in text (you would get an IndexOutOfRangeException when trying to access index 1). Also, you can use the Contains method on the array of lecturer names to simplify your where condition:

You could address these by doing something like:

public IEnumerable<Student> GetStudentBySelectedLecturer(List<Student> students,
    string lecturer)
{
    if (students == null || lecturer == null) return null;

    var lecturerName = lecturer.Split(' ');

    return from student in students
        where lecturerName.Contains(student.LecturerFirstName) &&
              lecturerName.Contains(student.LecturerLastName)
        select student;
}

last of us fan · Answer 2 · 2020-05-01T14:01:44.237

This is the exact same output of your issue, only using lambda expressions.

    studentListBySelectedLecturer = (from stud in linkedList
              where stud.LecturerFirstName == lecturerInformation[0] &&
              stud.LecturerLastName == lecturerInformation[1] ||
              stud.LecturerFirstName == lecturerInformation[1] &&
              stud.LecturerLastName == lecturerInformation[0]
              select stud).ToList();

    return studentListBySelectedLecturer;

Convert lambda expression into linq c#

2 Answers2