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
– Sebastian Ðymel, Commented Jun 11, 2013 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? — CodeCaster
– CodeCaster, Commented Jun 11, 2013 at 15:19

Haney · Accepted Answer · 2019-01-23 15:12:58Z

1242

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, 2019 at 15:12

answered Jun 11, 2013 at 15:15

Haney

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6 Comments

James Over a year ago

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.

azrosen92 Over a year ago

How do I check what version of C# I'm using or change it?

Haney Over a year ago

The project's properties will indicate the target version of the framework.

James Over a year ago

The version of Visual Studio you are using is usually a good indicator - see here for reference.

Haney Over a year ago

@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.

|

Peter Mortensen · Accepted Answer · 2021-08-18 10:55:28Z

363

+250

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, 2021 at 10:55

Peter Mortensen

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answered Feb 10, 2015 at 14:58

Vikram Kumar

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5 Comments

Maxter Over a year ago

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" },

Pablo Mariante Over a year ago

Works in c# 3.1 too. var dict = new Dictionary<string, double> { ["Abc"] = 2d }

duyn9uyen Over a year ago

That's a new syntax I wasn't familiar with. Thanks.

Vimes Over a year ago

Note, on duplicate keys this syntax does not throw whereas the other does (doc)

Sasino Over a year ago

I didn't know this syntax, thanks. It makes it easy to copy and paste dictionaries of data from other languages such as Lua.

Peter Mortensen · Accepted Answer · 2021-08-18 12:43:53Z

52

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, 2021 at 12:43

Peter Mortensen

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answered May 16, 2017 at 15:01

Debendra Dash

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1 Comment

Antony Booth Over a year ago

The ReSharper answer.

Peter Mortensen · Accepted Answer · 2021-08-18 10:56:26Z

50

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, 2021 at 10:56

Peter Mortensen

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answered Mar 11, 2015 at 22:38

Brendan

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2 Comments

Peter Mortensen Over a year ago

For what versions of C#? Was it there with the first version or was it introduced later?

MikeTeeVee Over a year ago

I like that you did not use var or Add().

Ed'ka · Accepted Answer · 2021-10-27 01:37:13Z

24

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 }
    };

answered Oct 27, 2021 at 1:37

Ed'ka

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Comments

Peter Mortensen · Accepted Answer · 2021-08-18 10:55:04Z

14

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

Overview of C# 3.0

edited Aug 18, 2021 at 10:55

Peter Mortensen

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answered Jun 11, 2013 at 15:15

Zbigniew

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Comments

Turbcool · Accepted Answer · 2020-10-28 20:08:37Z

5

With С# 6.0

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

edited Oct 28, 2020 at 20:08

Turbcool

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answered Feb 17, 2020 at 10:51

amesh

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2 Comments

TylerH Over a year ago

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.

amesh Over a year ago

@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.

nalka · Accepted Answer · 2025-05-14 13:07:20Z

2

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"
  }
}

edited May 14 at 13:07

nalka

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answered Feb 7, 2023 at 7:50

Namig Hajiyev

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