Question

Assume I have the following information in a flat format, for example a list of objects:

List<Line> lines = new List<Line>
                                   {
                                       new Line{Id = 1, Level = 0},
                                       new Line{Id = 2, Level = 1},
                                       new Line{Id = 3, Level = 1},
                                       new Line{Id = 4, Level = 2},
                                       new Line{Id = 5, Level = 2},
                                       new Line{Id = 6, Level = 1},
                                       new Line{Id = 7, Level = 1},
                                       new Line{Id = 8, Level = 2},
                                       new Line{Id = 9, Level = 1}
                                   };

Each object has an id and a level. What I want to end up with a nested list. For this I have a class which can have a list of children, based on the level.

public class NestedLine
    {
        public int Id;
        public List<NestedLine> Children = new List<NestedLine>();
    }

What’s the easiest way to convert that flat list into a nested list?

EDIT: The only information on how to construct the list is the order of the lines and the level. This should be the result:

1
--2
--3
  --4
  --5
--6
--7
  --8
--9

Answer 1

Here is my attempt.

Calling code

List<Line> lines = new List<Line>
                           {
                               new Line{Id = 1, Level = 0},
                               new Line{Id = 2, Level = 1},
                               new Line{Id = 3, Level = 1},
                               new Line{Id = 4, Level = 2},
                               new Line{Id = 5, Level = 2},
                               new Line{Id = 6, Level = 1},
                               new Line{Id = 7, Level = 1},
                               new Line{Id = 8, Level = 2},
                               new Line{Id = 9, Level = 1}
                           };

NestedLine nestedLine = Recusrsive(lines, 0);

Recursive Method

private NestedLine Recusrsive(List<Line> lines, int listPos)
{
    NestedLine retVal = new NestedLine();
    Line line = lines[listPos];

    retVal.Id = line.Id;

    for (int iItem = listPos + 1; iItem < lines.Count; iItem++)
        if (lines[iItem].Level == line.Level + 1)
            retVal.Children.Add(Recusrsive(lines, iItem));
        else if (lines[iItem].Level <= line.Level) return retVal;

    return retVal;
}