Succinct syntax for initializing list of lists

Question

Is there a concise syntax for intializing lists of lists in C#?

I tried

new List<List<int>>{
    {1,2,3},
    {4,5},
    {6,7,8,9}
};

But I get an error 'No overload for method 'Add' takes 3 arguments'

Edit: I know about the long syntax

 new List<List<int>>{
    new List<int>           {1,2,3},
    new List<int>           {4,5},
    new List<int>           {6,7,8,9}
};

I was just searching for something pithier.

Possible duplicate question: http://stackoverflow.com/questions/665299/are-2-dimensional-lists-possible-in-c — , Nov 27 '12 at 14:28
Not an answer but you could do something like this if you were using arrays: `new List { new[] { 1, 2, 3 }, new[] { 4, 5, 6 } };` — Şafak Gür, Mar 05 '14 at 08:27

score 6 · Answer 1 · answered Nov 27 '12 at 14:27

6

No, you need new List<int> for each:

var lists = new List<List<int>>() { 
    new List<int>{1,2,3},
    new List<int>{4,5},
    new List<int>{6,7,8,9}
};

answered Nov 27 '12 at 14:27

Tim Schmelter

score 3 · Accepted Answer · answered Aug 28 '22 at 17:09

With the introduction of target-typed new expressions in C# 9.0/.NET 5, you can now create a List<List<T>> more succinctly as follows:

new List<List<int>>{
    new () {1,2,3},
    new () {4,5},
    new () {6,7,8,9}
};

This works with dictionary initializers as well, e.g.

new List<Dictionary<string, int>>{
    new () {{"foo", 1}, {"bar", 2}}
};

or

new List<Dictionary<string, int>>{
    new () {["foo"] = 1, ["bar"] = 2}
};

2 Answers2