OmegaMan's Musings

(Update 5/16/2011: Fixed mispelling)
I ran across a situation where the code I was working on had an enum with values and I needed to display a user friendly text which was related to the enum but not the enum’s actual text value.

The standard way of mapping values across cultures is to create a localized resource file(s) (.resx) and to put in string key and a string value, where the value will be shown. The code can then do an if check to map between the two; but that gets laborious real quick. It would be better to have a dictionary where the enum is the key and the value is the value of the resources file.

The following snippet of code takes in an enum and its corresponding resource resx data and creates that dictionary. See the section Steps to Test for an example of its usage.

/// <summary>
/// Take an enum and a created corresponding resx resource file and join the two together 
/// into a dictionary. The dictionaries key is the actual enum and the value is the user readable text
/// found in the value of the resource file.
/// </summary>
/// <typeparam name="T">The Enum type which contains the target enums</typeparam>
/// <param name="rm">The .resx resource's manager which contains the mapped text</param>
/// <returns>A dictionary whose key is the enum and the result is the mapped text in the resource file.</returns>
public static Dictionary<T, string> LoadResourceEnumMappings<T>( ResourceManager rm )  
{
    T[] eValues = (T[])System.Enum.GetValues( typeof( T ) ); // Gets the actual values of the enum (T) type

    // Puts those into a local dictionary/hash for use in later.
    var dictEnum = eValues.ToDictionary( it => it.ToString(), it => it ); 

    // Work through the key value pairs (KVP) of the resource set and marry them
    // to a new dictionary where the key is the enum and the value output is the user string
    // as found in the resource's value of its kvp.
    return rm.GetResourceSet( Thread.CurrentThread.CurrentCulture, true, false )
             .OfType<DictionaryEntry>()
             .ToDictionary( kvp => dictEnum[kvp.Key.ToString()], kvp => kvp.Value.ToString() );

}

NOTES

• One can have more resource keys than enums and the above will work. But if there are more enums than resource keys, the above code will throw a KeyNotFound exception.

Enumerate the Embedded Resource

The above code uses the ability to enumerate or iterate the resource file by calling GetResourceSet. That calls returns a Dictionary entry which has the key value pair of the resource file and could be used with a foreach.

Steps To Test

1. Create console application
2. Create enum named MappedValues with these enums : Alpha, Beta, Gamma.

   public enum MappedValues
   {
       Alpha,
       Beta,
       Gamma
   }

3. Create Resource File named UserText.Resx with these values: 

Test as such with this code by calling EnumMapper.Usage():

public static class EnumMapper
{
    /// <summary>
    /// This is just for show and not meant for production.
    /// </summary>
    public static void Usage()
    {
        try
        {
            Console.WriteLine( "Load resource and show: " + UserText.Alpha );

            Dictionary<MappedValues, string> mapped = LoadResourceEnumMappings<MappedValues>( UserText.ResourceManager );

            Console.WriteLine( mapped[MappedValues.Alpha] );

            Console.WriteLine( mapped[MappedValues.Beta] );

            Console.WriteLine( mapped[MappedValues.Gamma] );
        }
        catch ( KeyNotFoundException )
        {
            Console.WriteLine("The Resource File has a key which is not found in the enum.");
        }

/* outputs (Note "first value" was shown to initialize the ResourceManager otherwise it would be null from GetResourceSet)
Load resource and show: First Value
First Value
Second Item
Third Wave
*/
    }

    /// <summary>
    /// Take an enum and a created corresponding resx resource file and join the two together 
    /// into a dictionary. The dictionaries key is the actual enum and the value is the user readable text
    /// found in the value of the resource file.
    /// </summary>
    /// <typeparam name="T">The Enum type which contains the target enums</typeparam>
    /// <param name="rm">The .resx resource's manager which contains the mapped text</param>
    /// <returns>A dictionary whose key is the enum and the result is the mapped text in the resource file.</returns>
    public static Dictionary<T, string> LoadResourceEnumMappings<T>( ResourceManager rm )  
    {
        T[] eValues = (T[])System.Enum.GetValues( typeof( T ) ); // Gets the actual values of the enum (T) type

        // Puts those into a local dictionary/hash for use in later.
        var dictEnum = eValues.ToDictionary( it => it.ToString(), it => it ); 

        // Work through the key value pairs (KVP) of the resource set and marry them
        // to a new dictionary where the key is the enum and the value output is the user string
        // as found in the resource's value of its kvp.
        return rm.GetResourceSet( Thread.CurrentThread.CurrentCulture, true, false )
                    .OfType<DictionaryEntry>()
                    .ToDictionary( kvp => dictEnum[kvp.Key.ToString()], kvp => kvp.Value.ToString() );

    }

}

This article demonstrates these concepts:

1. Regex extraction of Key Value pairs and placing them into named capture groups.
2. Linq extraction of the Key Value pairs extracted from the matches of Regex.
3. Dictionary creation from Linq using the ToDictionary method.

I answered this on the MSDN forums, the user had this data in key value pairs delimited by the pipe:

abc:1|bbbb:2|xyz:45|p:120

Keys values separators

The need was to get the keys and values into a dictionary. The following code uses named regex group matches which are used in Linq to extract the keys and their values. Once that is done within the linq the extended method ToDictionary is used to create the dictionary on the fly. Here is the code:

string input = "abc:1|bbbb:2|xyz:45|p:120";
string pattern = @"(?<Key>[^:]+)(?:\:)(?<Value>[^|]+)(?:\|?)";

Dictionary<string, string> KVPs
    = ( from Match m in Regex.Matches( input, pattern )
      select new
      {
          key = m.Groups["Key"].Value,
          value = m.Groups["Value"].Value
       }
       ).ToDictionary( p => p.key, p => p.value );

foreach ( KeyValuePair<string, string> kvp in KVPs )
    Console.WriteLine( "{0,6} : {1,3}", kvp.Key, kvp.Value );

/* Outputs:
 abc :   1
bbbb :   2
 xyz :  45
  p  : 120
 */

>(Post Updated 4/2/2011 : Added extra example)

I love the generic Dictionary collection so much, I think that Microsoft might charge me usage on it. Here I present some of the things that I have learned which I call the tribal knowledge of the class.

The first use of the Dictionary was found in .Net 1 HashTable class. That class is a dictionary for storing lists with keys and has the ubiquitously Key Value Pair. With .Net 2 the generic class Dictionary was used, less upfront functionality, but same concepts; data in key value pairs.

While the old hash table could be sorted the dictionary cannot. So how does one sort? The Dictionary is just two lists under the covers. One is for keys and one is for values. Operations don’t go to the hash table but to the lists. Once you remember that and understand it, the obtuseness of the Dictionary goes away…

Sorting

Ok, so we can sort…but one complaint or question found in the MSDN forums that I have run into is that, the Hashtable could be sorted because it exposed IComparer and its cousin the Dictionary does not! How does one get around that?

As mentioned one must think of what a dictionary really is…just two lists. There are two properties exposed on the Dictionary and those are the Keys and Values. Those are shown to the world as ValueCollection and that my friends is the entry pass into the club. One of the interfaces that is exposed is the ValueCollection and it adheres to the ICollection. Bingo! With that we can do sorting! Here is the code snippet:

Dictionary<int, string> myDict = new Dictionary<int, string>()
            {
                { 2, "This" },
                { 1, "is" },
                { 5, "radio" },
                { 12, "clash" },
            };

List<string> song = new List<string>( myDict.Values );

song.Sort();

// This writes out: "clash is radio This"
Console.WriteLine( string.Join( " ", song.ToArray() ) );

Enumerating over a Dictionary

Sometimes the need is there to run through a dictionary and show the keys and values. When enumerating over a Dictionary it returns a Key Value Pair object. That object holds the key and the value.

Dictionary<string, string> ColumnValuesHash = new Dictionary<string, string>()
// ... load with values...
foreach (KeyValuePair entry in ColumnValuesHash)
    Console.WriteLine("{0}: {1}", entry.Key, entry.Value);

Dictionary of Dictionaries

I have used this gem many times. Create a top level dictionary that will hold other dictionaries…its not as bad as it sounds.

Dictionary<int, string> myStringHash = new Dictionary<int, string>();

myStringHash.Add(41,      "Jabberwocky");
myStringHash.Add(8675309, "Jenny");

Dictionary< string, Dictionary<int, string>> myDicts = new Dictionary<string, Dictionary<int, string>>();

myDicts.Add("Test", myStringHash);

Console.WriteLine( myDicts["Test"][8675309] ); // Prints Jenny

Notice how easy it is to drill down via indexes off of each dictionary.

Dictionary Meets Linq and Gets Sorted

Here is how you can access the dictionary, sort it and enumerate it all in Linq. We will take our above example and do it

Dictionary<int, string> myDict = new Dictionary<int, string>()
                     {
                         { 2, "This" },
                         { 1, "is" },
                         { 5, "radio" },
                         { 12, "clash" },
                     };

var sorted = from item in myDict
             orderby item.Value ascending
             select item.Value;

// This writes out: "clash is radio This"
Console.WriteLine( string.Join( " ", sorted.ToArray() ) );

Extra Example (Loading on the fly and Linq extension Select Many)

Dictionary<string, Dictionary<int, string>> TopLevel = new Dictionary<string, Dictionary<int, string>>()
{
    {
        "Dictionary 1",
        new Dictionary<int, string>()
                                    { // Sub "dictionary 1" contains two objects
                                        {41, "The Meaning of Life" },
                                        {90125, "Owner of a Lonely Heart"}
                                    }
    },

    {

        "Dictionary 2",
        new Dictionary<int, string>()
                                    { // Sub "Dictionary 2" contains one object
                                        {8675309, "Jenny!" }
                                    }

    }

};

Console.WriteLine(TopLevel["Dictionary 1"][41]);      // Prints out "The Meaning of Life!"

//     Console.WriteLine(TopLevel["Dictionary 1"][8675309]); // Fails and would throw an exception! That is in Dictionary 2!

// Use selectmany to grab all sub objects
// (which are a Key value pair of KVP<string, Dictionary<int, string>)
// and return the value (the sub dictionaries) and combine
// all the those dictionaries from both sub dictionary into one IEnumerable KVP.
TopLevel.SelectMany( dict => dict.Value ) // Gets all the DIctionary<int, string> pairs between both dictionaries
        .ToList() // Convert from IEnumerable to list so we can do the for each below
        .ForEach( kvp => Console.WriteLine( "{0} is {1}", kvp.Key, kvp.Value ) ); // Outputs the lowest dictionaries.

/* above outputs
41 is The Meaning of Life
90125 is Owner of a Lonely Heart
8675309 is Jenny!
*/

Hope this helps!