根据字符串开头的字符串列表创建子列表

Question

Fist time posting, so forgive me on formatting... I have a text file that I've read in using File.ReadLines() and stored sequentially to a List. I then want to find the first instance of a string that starts with "Student". Then I want to get all of the strings in the list up to the next instance of a string that starts with "Student" and stop just before it. Copy those strings to a sub list, and then rinse and repeat until the end of the file is reached.

Example of text file:

something on line 1

something on line 2

Student ...: Joe Smith

Id...: 12345

Major...: Math

unknown number of more lines

Student ...: Jane Smith

Id...: 54321

Major...: Nursing

more lines

Student ...: John Doe

Id...: 11223

Major: Anatomy

even more lines.

I'd like the list of lines per student to look like this:

Student 1

Student...: Joe Smith

Id...: 12345

Major...: Math

unknown number of more lines

Student 2

Student...: Jane Smith

Id...: 54321

Major...: Nursing

more lines

I've used a foreach to iterate the lines. Each line is added to a new list. When I find a string that starts with "Student" then I create a new student object and store those lines in the sub list to it. Then I clear the sublist and then continue on with the foreach, creating new student objects.

Current issues I miss the last student. I know I could have the if statement that checks if the current line starts with "Student" to include checking if the current line is the last line in the list, but I feel there has to be a better/fast way to do this.
I have to add the && lines.Count > 3 because there are a few lines before the first instance of "Student" which I want to skip.

Linq examples would be greatly appreciated.

List<Student> students = new List<Student>();
List<string> lines = File.ReadLines(args[0]).ToList();  
List<string> student_lines = new List<string>();
foreach(string line in lines) 
{ 
    if(line.StartsWith("Student...", StringComparison.OrdinalIgnoreCase) && lines.Count > 3) 
    {
        students.Add(new Student(student_lines)); 
        student_lines.Clear(); 
    } 
    lines.Add(line)
}

Answer 1

Try this:

var results =
    lines
        .Aggregate(new[] { new List<string>() }.ToList(), (a, x) =>
        {
            if (x.StartsWith("Student"))
            {
                a.Add(new List<string>());
            }
            a.Last().Add(x);
            return a;
        })
        .Skip(1)
        .Select(x => new Student(x))
        .ToList();

From your sample data I get this:

Answer 2

Something like this

if (args.Length < 1) return;                // optional check if any args

string text = File.ReadAllText(args[0]);

string[] parts = text.Split(new[] { "Student" }, 0);

string[][] lines = Array.ConvertAll(parts, part => part.Split(new[] { '\r', '\n' }, 1));

Debug.Print(lines[1][1]);        // "Id...: 12345"

Answer 3

It is really vague what you are trying to do but here is a very basic example of what I think you are doing.

Now the only thing you need to do is change the fileName param.

static void Main(string[] args)
{
    string line = null;
    Student student = null;
    IList<Student> students = new List<Student>();
    using (var fileReader = new StreamReader(fileName))
    {
        while ((line = fileReader.ReadLine()) != null)
        {
            if (string.IsNullOrWhiteSpace(line))
                continue; //continue execution on extra lines
            if(line.StartsWith("Student...", StringComparison.CurrentCultureIgnoreCase))
            {
                student = new Student();
                students.Add(student);
            }

            if (student != null)
                student.Lines.Add(line);


        }

        fileReader.Close();
    }
}

class Student
{
    public IList<string> Lines { get; } = new List<string>();
}

In a nutshell all this little program does is starts reading a file line by line (note while ((line = fileReader.ReadLine()) != null) will set the value of line to the next line in the file or null when the file has been completely read.

Next it checks for empty lines (we dont care about empty lines so we move on)

We then check if the line startsith Student... now we are using StringComparison.CurrentCultureIgnoreCase so we can compare case insensitive.

If this is a Student line, we then create a new student and Add() it to our students collection.

Finally as long as student is not null we can add the contents of line to the student .Lines property.