List, nested. A List can have elements of List type. This is a jagged list, similar in syntax to a jagged array. Lists are not by default multidimensional in C#.
2D list solution. To store more complex shapes of data, we can develop multidimensional Lists. We use an easily-developed and expandable data structure.
Requirements. Consider this shape: the first row has 3 elements, the next row just has 1, and then we have a row with 4 elements. We require a nested list solution that allows this data.
0 1 2
2
1 2 3 4
Example code. The C# List provides an underlying and internal array where it stores its elements. But it always specifies a one-dimensional and zero-based array in its internal structure.
using System;
using System.Collections.Generic;
class Program
{
static void Main()
{
// Part 1: add rows and columns to the List.List<List<int>> list = new List<List<int>>();
var rand = new Random();
for (int i = 0; i < 3; i++)
{
// Put some integers in the inner lists.List<int> sublist = new List<int>();
int top = rand.Next(1, 4);
for (int v = 0; v < top; v++)
{
sublist.Add(rand.Next(1, 5));
}
// Add the sublist to the top-level List.
list.Add(sublist);
}
// Display the List.
Display(list);
}
static void Display(List<List<int>> list)
{
// Part 2: loop over and display everything in the List.
Console.WriteLine("Elements:");
foreach (var sublist in list)
{
foreach (var value in sublist)
{
Console.Write(value);
Console.Write(' ');
}
Console.WriteLine();
}
// Part 3: display element.
Console.WriteLine("Element at 1, 0:");
Console.WriteLine(list[1][0]);
// Part 4: display total count.
int count = 0;
foreach (var sublist in list)
{
count += sublist.Count;
}
Console.WriteLine("Count:");
Console.WriteLine(count);
}
}Elements:
1 3
2 2 2
2
Element at 1, 0:
2
Count:
6
A discussion. As for performance, a nested List is relatively fast. It internally uses zero-based arrays, and the List type itself is fast.
But Adding another layer of abstraction and creating a nested class may be desirable.
Note This can help reduce the amount of complexity and syntax confusion at the calling sites.
Tip Another option is to encapsulate the List<List<T>> into a separate class. This could be better for real-world programs.
A summary. We used a nested List that is essentially a jagged or 2D List data type with the generic List class. The code here is not ideal. But it helps in prototyping or experimental work.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
