C# Access Dictionary value from array-CodePudding

Say, I have an string[] of undetermined length, and a Dictionary<string, object>, which more Dictionaries of its exact type (or other types, which doesn't matter here).

Now I want to change a value in a Dictionary in a Dictionary ... in my Dictionary depending on my string array.

Here's a little Visualisation:

string[]: { "Human", "Legs", "Walking" }

Dictionary: 
   ↳ Key "Human":
       ↳ Key "Legs":
           ↳ Key "Walking"

I wanna set the value of the key "Walking" in this example (lets just say to true)

Now my question is: How do i achive this in C#?

Any answers will be appreciated, please excuse me if i am overthinking this.

CodePudding user response：

Because you're using Object for TValue you'll need to use the x is T v operator to test if an Object is another dictionary, e.g. if( x is Dictionary<String,Object> dict ).

The difficulty here is that you can't use x is T v with a strongly-typed T because IReadOnlyDictionary<K,V> is not covariant over V, even when you know what K is (as C# and .NET do not support partially-closed generic types).

...but if you don't need/want exactly-typed types and provided that all dictionary objects in your graph are always exactly Dictionary<String,Object> (and not Dictionary<String,Int32> or Dictionary<String,String>) then you can do this:

String[] dictPath = new[] { "Human", "Legs", "Walking" };

Dictionary<String,Object> dictGraph = ...

Object humanLegsWalkingValue = GetValueAtPath( dictGraph, dictPath );

//

static Object? GetValueAtPath( Dictionary<String,Object> root, String[] dictPath )
{
    List<String> breadcrumbs = new List<String>(); // For reporting errors.
    
    Dictionary<String,Object> current = root;
    foreach( String name in dictPath )
    {
        breadcrumbs.Add( name );
    
        if( current.TryGetValue( name, out Object? value ) )
        {
            if( value is Dictionary<String,Object> dict )
            {
                current = dict;
            }
            else
            {
                if( breadcrumbs.Count == dictPath.Length )
                {
                    return value;
                }
                else
                {
                    String valueType = value is null ? "null" : value.GetType().FullName;
                    const String MSG_FMT = "Value at \"{0}\" is not a dictionary but is actually {1}, therefore \"{2}\" is unreachable."

                    throw new InvalidOperationException( String.Format( MSG_FMT, String.Join( ".", breadcrumbs ), valueType, String.Join( ".", dictPath ) ) );
                }
            }
        }
        else
        {
            const String MSG_FMT = "Could not find name \"{0}\" at \"{1}\" therefore \"{2}\" is unreachable."

            throw new KeyNotFoundException( String.Format( MSG_FMT, name, String.Join( ".", breadcrumbs ), String.Join( ".", dictPath ) ) );
        }
    } 

}

To set a value, it uses almost the exact same logic to walk the dictionary-graph, except it stops 1-step short of the end of dictPath and uses that to set an entry in current:

static void SetValueAtPath( Dictionary<String,Object> root, String[] dictPath, Object newValue )
{
    List<String> breadcrumbs = new List<String>(); // For reporting errors.
    
    Dictionary<String,Object> current = root;
    foreach( ( String name, Int32 idx ) in dictPath.Select( ( n, i ) => ( n, i ) ) )
    {
        breadcrumbs.Add( name );
    
        if( idx == dictPath.Length - 1 )
        {
            current[ name ] = newValue;
            return;
        }
        else if( current.TryGetValue( name, out Object? value ) )
        {
            if( value is Dictionary<String,Object> dict )
            {
                current = dict;
            }
            else
            {
                String valueType = value is null ? "null" : value.GetType().FullName;
                const String MSG_FMT = "Value at \"{0}\" is not a dictionary but is actually {1}, therefore {2} is unreachable."

                throw new InvalidOperationException( String.Format( MSG_FMT, String.Join( ".", breadcrumbs ), valueType, String.Join( ".", dictPath ) );
            }
        }
        else
        {
            const String MSG_FMT = "Could not find name \"{0}\" at \"{1}\" therefore \"{2}\" is unreachable."

            throw new KeyNotFoundException( String.Format( MSG_FMT, name, String.Join( ".", breadcrumbs ), String.Join( ".", dictPath ) ) );
        }
    } 

}

CodePudding user response：

This might not be a (direct) answer to your question:


string[] strs = new string[] { "Human", "Legs", "Walking" };

Dictionary<string,string> dict = new Dictionary<string, string>();

for(int i=0; i<strs.Length; i  ) {
    dict.Add(strs[i],(i>0?strs[i-1]:""));
}

string find = "Human";

if(dict.ContainsKey(find)) {
    System.Console.WriteLine($"Hello: {find}");
    foreach (var item in dict.Where(x=>x.Value==find))
    {
        System.Console.WriteLine($"You have: {item.Key}");
        foreach (var item2 in dict.Where(x=>x.Value==item.Key)) 
        {
            System.Console.WriteLine($"Which can make you: {item2.Key}");
        }
    }
}
else
{
    System.Console.WriteLine($"Could not find: {find}");
}

output:

Hello: Human
You have: Legs
Which can make you: Walking

NOTE: It's pretty unclear why the title of your question has Dictionary and you start defining an array (string[]).