Accessing key from value

Question

I want to access key from value. and I am able to access value from key. My json file look as

{
    "screen": {
        "0": "42x11",
        "1": "16x16",
        "2": "40x30",
        "3": "32x32",
        "4": "42x32",
        "5": "48x32",
        "6": "60x40",
        "7": "150x40",
        "8": "84x48"
    },
    "os": {
        "0": {
            "versions": {
                "1": {
                    "name": "10"
                },
                "2": {
                    "name": "8"
                },
                "3": {
                    "name": "7"
                }
            },
            "name": "Windows"
        }
    },
    "app": {
        "1": {
            "name": "javaScript1",
            "versions": {
                "1": {
                    "name": "1.0"
                }
            }
        }
    }

}

I have parsed the file with the help of JavaScriptSerializer as.

public void deserialize_metadata()
{
   using (StreamReader r = new StreamReader("C:\\Users\\vikash.kumar\\Desktop\\metadatainfo.json"))
   {
        var json = r.ReadToEnd();
        var jss = new JavaScriptSerializer();
        var dict = jss.Deserialize<Dictionary<string, dynamic>>(json);
        Console.WriteLine("dict" + dict["screen"]["0"]);    //o/p - 42x11
        Console.WriteLine("dict" + dict["app"]["1"]["name"]); //o/p - javaScript1
      }
}

It works fine when we want to access value from key.

How we can access key from value by this process?

In that case you should add the information into the question. — Ankush, Aug 21 '18 at 09:32
@PatrickHofman I have tried to use as dict["screen"].value then .value was throwing error — Vikash Kumar, Aug 21 '18 at 09:40
I have used as **if(dict["screen"].value.equals("42x11"))** and exception occured as **Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: ''System.Collections.Generic.Dictionary' does not contain a definition for 'value'' ** — Vikash Kumar, Aug 21 '18 at 09:46
`Value` and `value` are different, C# is **case sensitive**. Also `dict["screen"]` should already return the "value" — Rafalon, Aug 21 '18 at 09:47
@Rafalon if i use just dict["screen"] in Console.WriteLine then ** System.Collections.Generic.Dictionary`2[System.String,System.Object] ** get printed — Vikash Kumar, Aug 21 '18 at 09:56
@Damien_The_Unbeliever How do you mean? If you mean where he's calling `var json = r.ReadToEnd();` in C#? This is strongly-typed because `ReadToEnd()` returns a string, so the type of `json` at compile time is `string`. Are you suggesting this might be contributing to the problem? https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/var — Trevor, Aug 21 '18 at 14:08
@Trevor - 4 hours ago, the OP removed their edit stating "There is no option to use .value and .key property in variable of var type.". It was to this I was objecting. It seemed to indicate they were at the point of confusion, often reached with people first learning about `var` in C# that it's somehow a different type rather than being a compiler trick that still leads to an actual type being selected for the variable. — Damien_The_Unbeliever, Aug 21 '18 at 14:10
@Damien_The_Unbeliever Fair enough, I didn't see it before the edit. I completely agree that it suggests confusion over how `var` works. — Trevor, Aug 21 '18 at 14:14

Rafalon · Accepted Answer · 2018-08-21T10:26:20.203

0

From the duplicate, try: dict["screen"].FirstOrDefault(x => x.Value == "42x11")?.Key

I added ?. to take care of the possibility that .FirstOrDefault can return null if there's no match. This way it won't throw an exception but only return null.

Edit

Console.WriteLine((dict["screen"] as Dictionary<string, dynamic>)
                      .First(x => x.Value == "16x16").Key);

edited Aug 21 '18 at 10:26

answered Aug 21 '18 at 09:54

Rafalon

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**Cannot use a lambda expression as an argument to a dynamically dispatched operation without first casting it to a delegate or expression tree type** error is showing at x=>x.value == "42x11" – Vikash Kumar Aug 21 '18 at 10:05
Oh right, that's because of the `dynamic` you used in your json deserializer. Maybe you could create a class that matches your json's format and explicitly tell that `dict["screen"]` is a `Dictionary` or just try to cast it this way (`var scr = dict["screen"] as Dictionary;` then `scr.FirstOrDefault(...)`) – Rafalon Aug 21 '18 at 10:07
Okay but how we can express app then,, – Vikash Kumar Aug 21 '18 at 10:09
You could do it like that: `Console.WriteLine((dict["screen"] as Dictionary).FirstOrDefault(x => x.Value == "16x16").Key);` – L_J Aug 21 '18 at 10:11
@VikashKumar this is a different question, but if your json isn't really dynamic, then maybe you should consider having a class with `screen`, `os`, and `app` **fields** having respectively `Dictionary`, `Dictionary` and `Dictionary` **types**. You would then access `dict.screen` instead of `dict["screen"]`. Or you could go further and completely remove `dynamic` – Rafalon Aug 21 '18 at 10:14
Thanks my problem is solved – Vikash Kumar Aug 21 '18 at 10:23

Accessing key from value

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