Proper way to initialize a C# dictionary with values

Question

I am creating a dictionary in a C# file with the following code:

private readonly Dictionary<string, XlFileFormat> FILE_TYPE_DICT
        = new Dictionary<string, XlFileFormat>
        {
            {"csv", XlFileFormat.xlCSV},
            {"html", XlFileFormat.xlHtml}
        };

There is a red line under new with the error:

Feature 'collection initilializer' cannot be used because it is not part of the ISO-2 C# language specification

What is going on here?

I am using .NET version 2.

Change targeted framework version or use the "old" way of initialization. — Sebastian Ðymel, Jun 11 '13 at 15:19
In what context do you place this code? A `.cs` file that gets compiled by Visual Studio, or in a `.cshtml`? Does your [project file have a `languageVersion` element](https://code.google.com/p/fast-member/issues/detail?id=1)? — CodeCaster, Jun 11 '13 at 15:19

Haney · Accepted Answer · 2019-01-23T15:12:58.967

1132

I can't reproduce this issue in a simple .NET 4.0 console application:

static class Program
{
    static void Main(string[] args)
    {
        var myDict = new Dictionary<string, string>
        {
            { "key1", "value1" },
            { "key2", "value2" }
        };

        Console.ReadKey();
    }
}

Can you try to reproduce it in a simple Console application and go from there? It seems likely that you're targeting .NET 2.0 (which doesn't support it) or client profile framework, rather than a version of .NET that supports initialization syntax.

edited Jan 23 '19 at 15:12

answered Jun 11 '13 at 15:15

Haney

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17

The issue is the version of C# the OP is using, object/collection initializers weren't introduced until C# 3.0. The detail as to why it didn't work before has already been [answered](http://stackoverflow.com/questions/459652/why-do-c-sharp-collection-initializers-work-this-way). – James Jun 11 '13 at 15:20
1

How do I check what version of C# I'm using or change it? – azrosen92 Jun 11 '13 at 15:33
3

The project's properties will indicate the target version of the framework. – Haney Jun 11 '13 at 15:35
The version of Visual Studio you are using is usually a good indicator - see here for [reference](http://stackoverflow.com/questions/247621/what-are-the-correct-version-numbers-for-c). – James Jun 11 '13 at 15:37
2

@James - Not reliably, however, as this person may be picking up some legacy work in a solution that was targeting 2.0 and isn't aware of it, for example. – Haney Jun 11 '13 at 15:46
if you're using .net 4.0 why not just write it with inline assembly? – Harry Aug 30 '23 at 11:09

score 333 · Answer 2 · edited Aug 18 '21 at 10:55

333

With C# 6.0, you can create a dictionary in the following way:

var dict = new Dictionary<string, int>
{
    ["one"] = 1,
    ["two"] = 2,
    ["three"] = 3
};

It even works with custom types.

edited Aug 18 '21 at 10:55

Peter Mortensen

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answered Feb 10 '15 at 14:58

Vikram Kumar

3,876
1
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28

1

I like your way betther, but take notes that it uses the exact same number of "boilerplate" characters per line (4) as the accepted answer with { "key2", "value2" }, – Maxter Sep 12 '18 at 15:50
1

Works in c# 3.1 too. var dict = new Dictionary { ["Abc"] = 2d } – Pablo Mariante Jan 22 '23 at 01:12
2

That's a new syntax I wasn't familiar with. Thanks. – duyn9uyen Apr 19 '23 at 13:25

score 45 · Answer 3 · edited Aug 18 '21 at 10:56

45

You can initialize a Dictionary (and other collections) inline. Each member is contained with braces:

Dictionary<int, StudentName> students = new Dictionary<int, StudentName>
{
    { 111, new StudentName { FirstName = "Sachin", LastName = "Karnik", ID = 211 } },
    { 112, new StudentName { FirstName = "Dina", LastName = "Salimzianova", ID = 317 } },
    { 113, new StudentName { FirstName = "Andy", LastName = "Ruth", ID = 198 } }
};

See How to initialize a dictionary with a collection initializer (C# Programming Guide) for details.

edited Aug 18 '21 at 10:56

Peter Mortensen

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answered Mar 11 '15 at 22:38

Brendan

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For what versions of C#? Was it there with the first version or was it introduced later? – Peter Mortensen Aug 18 '21 at 10:57
I like that you did **_not_** use `var` or `Add()`. – MikeTeeVee Nov 09 '21 at 19:29

score 45 · Answer 4 · edited Aug 18 '21 at 12:43

45

Suppose we have a dictionary like this:

Dictionary<int, string> dict = new Dictionary<int, string>();
dict.Add(1, "Mohan");
dict.Add(2, "Kishor");
dict.Add(3, "Pankaj");
dict.Add(4, "Jeetu");

We can initialize it as follows.

Dictionary<int, string> dict = new Dictionary<int, string>
{
    { 1, "Mohan" },
    { 2, "Kishor" },
    { 3, "Pankaj" },
    { 4, "Jeetu" }
};

edited Aug 18 '21 at 12:43

Peter Mortensen

30,738
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answered May 16 '17 at 15:01

Debendra Dash

5,334
46
38

The ReSharper answer. – Antony Booth May 22 '19 at 19:16

score 14 · Answer 5 · edited Aug 18 '21 at 10:55

14

Object initializers were introduced in C# 3.0. Check which framework version you are targeting.

Overview of C# 3.0

edited Aug 18 '21 at 10:55

Peter Mortensen

30,738
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answered Jun 11 '13 at 15:15

Zbigniew

27,184
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score 12 · Answer 6 · answered Oct 27 '21 at 01:37

Note that C# 9 allows Target-typed new expressions so if your variable or a class member is not abstract class or interface type duplication can be avoided:

    private readonly Dictionary<string, XlFileFormat> FILE_TYPE_DICT = new ()
    {
        { "csv", XlFileFormat.xlCSV },
        { "html", XlFileFormat.xlHtml }
    };

score 5 · Answer 7 · edited Oct 28 '20 at 20:08

5

With С# 6.0

var myDict = new Dictionary<string, string>
{
    ["Key1"] = "Value1",
    ["Key2"] = "Value2"
};

edited Oct 28 '20 at 20:08

Turbcool

84
8

answered Feb 17 '20 at 10:51

amesh

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Your answer (before it was edited by Turbcool) was an exact copy of the accepted answer by Haney. Please ensure future answers provide *new* solutions to questions. – TylerH Dec 08 '20 at 22:23
@TylerH The answer was unique, as I have suggested the indexer-based approach(Used variables from accepted answer). But the answer was not a copy. Please refer to the edit history. – amesh Oct 20 '21 at 06:31

score 0 · Answer 8 · answered Feb 07 '23 at 07:50

Here is an example of Dictionary with Dictionary value

            Dictionary<string, Dictionary<int, string>> result = new() {
                ["success"] = new() {{1, "ok"} ,  { 2, "ok" } },
                ["fail"] = new() {{ 3, "some error" }, { 4, "some error 2" } },
            };

which is equivalent to this in JSON :

{
  "success": {
    "1": "ok",
    "2": "ok"
  },
  "fail": {
    "3": "some error",
    "4": "some error 4"
  }
}

Proper way to initialize a C# dictionary with values

8 Answers8

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