How to construct an instance of Dictionary<string, List<string>>

Question

I am trying to code in C#, but I find that I can't construct an instance in this way like C++:

Dictionary<string, List<string>> FirSet =
    new Dictionary<string, List<string>>() {
        { "a", {"ab", "abc"} },
        { "b", {"bc", "bcd"} }
    };

You need new List<string>() before your list items. So { "a", {"ab", "abc"} } should become { "a", new List<string>() {"ab", "abc"} } — maccettura
– maccettura, Commented Apr 16, 2018 at 14:54
Do you really need a List<string> or can it be a string[] array? You can use that initialization syntax with arrays. For lists, you need to new one up for each dictionary value. — itsme86
– itsme86, Commented Apr 16, 2018 at 14:54
@itsme86 wouldnt you still need to new up an array in that case? new [] { "some", "example" }? — maccettura
– maccettura, Commented Apr 16, 2018 at 14:55

dmigo · Accepted Answer · 2018-04-16 15:02:14Z

6

You have to initiate the lists within the dictionary with new List<string>()

Here how it should work:

Dictionary<string, List<string>> FirSet = new Dictionary<string, List<string>>()
{
    { "a", new List<string> { "ab", "abc" }},
    { "b", new List<string> { "bc", "bcd" }}
};

edited Apr 16, 2018 at 15:02

dmigo

3,0555 gold badges47 silver badges67 bronze badges

answered Apr 16, 2018 at 14:57

Lucion

1025 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

DavidG Over a year ago

Minor point, but if you're going to drop the () (which I prefer) from the latter list creation, you should also do it for the first one.

Zohar Peled Over a year ago

Since our answers are (now) the same, I've deleted mine and upvoted yours.

Lucion Over a year ago

@DavidG yes you are completaly right, its unnecessary, but since its possible i wanted to show both ways. might help FreAk Apoint in the future

Lucion Over a year ago

@ZoharPeled thank you, to be fair i just threw the answer out, dmigo was so kind to format it like it is

Philippe · Accepted Answer · 2018-04-16 15:08:23Z

2

    var firSet =
        new Dictionary<string, List<string>>()
        {
            { "a", new List<string>() {"ab", "abc"} },
            { "b", new List<string>() {"bc", "bcd"} }
        };

You can also use the C# 6.0 syntax:

    var firSet =
        new Dictionary<string, List<string>>()
        {
            ["a"] = new List<string> {"ab", "abc"},
            ["b"] = new List<string> {"bc", "bcd"}
        };

And if you feel particularly lazy and you don't want to type all these new List<string> you can always do this:

    var firSet =
        new Dictionary<string, string[]>()
        {
            { "a", new[] {"ab", "abc"} },
            { "b", new[] {"bc", "bcd"} }
        }
        .ToDictionary(i => i.Key, i => i.Value.ToList());

edited Apr 16, 2018 at 15:08

answered Apr 16, 2018 at 14:58

Philippe

4,0613 gold badges44 silver badges57 bronze badges

Collectives™ on Stack Overflow

How to construct an instance of Dictionary<string, List<string>>

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related