searching list of objects

I have a List of Student objects as such: List<StudentInfo>. Now the StudentInfo object has certain parameters such as Name, ID and Attendance. I want to search the list by two things. I want to search by student Name and student id. The query should return the Attendance count for the studentInfo object. Here is what i have tried:

return studentInfoList
    .Select((item) => new { value = item })
    .Where(item => item.value.StudentName.Equals(name) 
                   &&开发者_运维知识库 item.value.StudentID.Equals(id))
    .Select(item => item.value.Attendance);

How can i do this?

Use Count() method:

return studentInfoList
    .Where(item => item.StudentName.Equals(name) 
          && item.StudentID.Equals(id))
    .Select(item => item.Attendance.Count());

// find student using conditions, suppose it may be only one
var student = studentInfoList
    .SingleOrDefault(item => item.StudentName.Equals(name)
        && item.StudentID.Equals(id));
// found
if (student != null)
{
    return student.Attendance;
}
else
{
    // not found
}

I would try this

return studentInfoList.First(s => s.Name == name && s.StudentId == id).Attendance

Why is studentId not enough to locate a student?

Your data structure is hard to understand, but I've tried to simplify it and clean up.

return studentInfoList
    .Single(si => si.StudentName == name || si.StudentID == id)
    .Attendance;

I've assumed you only need the name or the id to find a student, not both. Also that Attendance is an integer, not an array. And that you need to make sure it is only for a single student, and if the student isn't found it should throw an exception.

// return the student with the given name and ID or null, if it cannot be found
StudentInfo student =
    studentInfoList.Where(item => item.StudentName == name 
                                   && item.StudentID == id).SingleOrDefault();

if (student == null) {
    // student not found
} else {
    return student.Attendance;
}

If you are talking the Attendance property of the item found, you just need:

var count = studentInfoList
    .Where(item => item.StudentName.Equals(name) && item.StudentID.Equals(id))
    .Select(item => item.Attendance).FirstOrDefault();