Create Dictionary(of Dictionary) using Grouping in Linq

Question

I know I could do this with loops (as a matter of fact, I currently am, but I am trying to learn / imporve my Linq skills and i also hope it will provide a more efficent sol

Answer 1

The three lists make things a bit difficult, but not impossible. Either you first zip the lists together as suggested by @fsimonazzi, or you base your query on the list indices rather than the list entries themselves. The result could look like this:

_(C#)

var result = Enumerable
    .Range(0, lstTeachers.Count)
    .GroupBy(i => lstTeachers[i])
    .ToDictionary(g => g.Key, g => g
        .GroupBy(i => lstStudentsSex[i])
        .ToDictionary(h => h.Key, h => h
            .Select(i => lstStudentName[i])
            .ToList()));

// result is Dictionary>>