Array of Lists in C#

1. Array of Lists With the List<T>[] Notation in C#
2. Array of Lists With the LINQ Method in C#

This tutorial will discuss the methods to create an array of lists in C#.

Array of Lists With the List<T>[] Notation in C#

The List<T>[] notation can be used to declare an array of lists of type T in C#. Keep in mind that this will only declare an array of null references. We still have to initialize each list at each index of the List<T>[] with the new keyword.

using System;
using System.Collections.Generic;

namespace array_of_lists {
  class Program {
    static void Main(string[] args) {
      List<int>[] arrayList = new List<int>[3];
      arrayList[0] = new List<int> { 1, 2, 3 };
      arrayList[1] = new List<int> { 4, 5, 6 };
      arrayList[2] = new List<int> { 7, 8, 9 };
      foreach (var list in arrayList) {
        foreach (var element in list) {
          Console.WriteLine(element);
        }
      }
    }
  }
}

Output:

1
2
3
4
5
6
7
8
9

In the above code, we declared and initialized the array of lists arrayList containing integer values with the List<T>[] notation and new keyword in C#. The above approach is ok for small arrays. But, if we have a large array, this approach can become very labor-intensive and can take a lot of code. This approach is only suitable for arrays with a smaller length.

Array of Lists With the LINQ Method in C#

The LINQ is used for integrating query functionality with the data structures in C#. We can use LINQ to declare and initialize an array of lists in C#.

using System;
using System.Collections.Generic;

namespace array_of_lists {
  class Program {
    static void Main(string[] args) {
      List<int>[] arrayList = new List<int> [3].Select(item => new List<int> { 1, 2, 3 }).ToArray();
      foreach (var list in arrayList) {
        foreach (var element in list) {
          Console.WriteLine(element);
        }
      }
    }
  }
}

Output:

1
2
3
1
2
3
1
2
3

In the above code, we declared and initialized the array of lists arrayList containing integer values with the List<T>[] notation and new keyword in C#. This method is less labor-intensive than the previous example for larger arrays, so it is more suitable for arrays with a larger length.