Convert IDictionary<string, string> keys to lowercase (C#)

Question

Hi, I've got a Method that gets a IDictionary as a parameter. Now I want to provide a method that retrieves the value from this dictionary, but it should be case-invariant.

So my solution to this right now was to have a static function that loops through the keys and converts them toLower() like this:

private static IDictionary<ILanguage, IDictionary<string, string>> ConvertKeysToLowerCase(
    IDictionary<ILanguage, IDictionary<string, string>> dictionaries)
{
    IDictionary<ILanguage, IDictionary<string, string>> resultingConvertedDictionaries 
        = new Dictionary<ILanguage, IDictionary<string, string>>();
    foreach(ILanguage keyLanguage in dictionaries.Keys)
    {
        IDictionary<string, string> convertedDictionatry = new Dictionary<string, string>();
        foreach(string key in dictionaries[keyLanguage].Keys)
        {
            convertedDictionatry.Add(key.ToLower(), dictionaries[keyLanguage][key]);
        }
        resultingConvertedDictionaries.Add(keyLanguage, convertedDictionatry);
    }
    return resultingConvertedDictionaries;
}

Now, this is ok, but still it's a pretty huge chunk of code that contradicts my idea of "clean and efficient". Do you know any alternatives to this so that the .ContainsKey() method of the dictionary doesn't differentiate between casing?

Answer 1

Yes - pass the Dictionary constructor StringComparer.OrdinalIgnoreCase (or another case-ignoring comparer, depending on your culture-sensitivity needs).

Jon

Answer 2

You could use the var keyword to remove some clutter. Technically the source remains the same. Also I would just pass and return a Dictionary<string, string> because you're not doing anything with that ILanguage parameter and make the method more reusable:

private static IDictionary<string, string> ConvertKeysToLowerCase(
    IDictionary<string, string> dictionaries)
{
    var convertedDictionatry = new Dictionary<string, string>();
    foreach(string key in dictionaries.Keys)
    {
        convertedDictionatry.Add(key.ToLower(), dictionaries[key]);
    }
    return convertedDictionatry;
}

... and call it like so:

// myLanguageDictionaries is of type IDictionary<ILanguage, IDictionary<string, string>>
foreach (var dictionary in myLanguageDictionaries.Keys)
{
  myLanguageDictionaries[dictionary].Value = 
      ConvertKeysToLowerCase(myLanguageDictionaries[dictionary].Value);
}

Answer 3

You could inherit from IDictionary yourself, and simply marshal calls to an internal Dictionary instance.

Add(string key, string value) { dictionary.Add(key.ToLowerInvariant(), value) ; }
public string this[string key]
{
    get { return dictionary[key.ToLowerInvariant()]; }
    set { dictionary[key.ToLowerInvariant()] = value; }
}
// And so forth.

Answer 4

LINQ version using the IEnumerable<T> extension methods:

        private static IDictionary<ILanguage, IDictionary<string, string>> ConvertKeysToLowerCase(
            IDictionary<ILanguage, IDictionary<string, string>> dictionaries)
        {
            return dictionaries.ToDictionary(
                x => x.Key, v => CloneWithComparer(v.Value, StringComparer.OrdinalIgnoreCase));
        }

        static IDictionary<K, V> CloneWithComparer<K,V>(IDictionary<K, V> original, IEqualityComparer<K> comparer)
        {
            return original.ToDictionary(x => x.Key, x => x.Value, comparer);
        }

Answer 5

System.Collections.Specialized.StringDictionary() may help. MSDN states:

"The key is handled in a case-insensitive manner; it is translated to lowercase before it is used with the string dictionary.

In .NET Framework version 1.0, this class uses culture-sensitive string comparisons. However, in .NET Framework version 1.1 and later, this class uses CultureInfo.InvariantCulture when comparing strings. For more information about how culture affects comparisons and sorting, see Comparing and Sorting Data for a Specific Culture and Performing Culture-Insensitive String Operations."

Answer 6

By using a StringDictionary the keys are converted to lower case at creating time.

http://simiansoftware.blogspot.com/2008/11/have-const-string-with-ui-description.html