OrderBy ignoring accented letters

Question

I want a method like OrderBy() that always orders ignoring accented letters and to look at them like non-accented. I already tried to override OrderBy() but seems I can't do that because that is a static method.

So now I want to create a custom lambda expression for OrderBy(), like this:

public static IOrderedEnumerable<TSource> ToOrderBy<TSource, TKey>(
    this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
    if(source == null)
        return null;

    var seenKeys = new HashSet<TKey>();

    var culture = new CultureInfo("pt-PT");
    return source.OrderBy(element => seenKeys.Add(keySelector(element)), 
                          StringComparer.Create(culture, false));
} 

However, I'm getting this error:

Error 2 The type arguments for method 'System.Linq.Enumerable.OrderBy<TSource,TKey>(System.Collections.Generic.IEnumerable<TSource>, System.Func<TSource,TKey>, System.Collections.Generic.IComparer<TKey>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

Seems it doesn't like StringComparer. How can I solve this?

Note:

I already tried to use RemoveDiacritics() from here but I don't know how to use that method in this case. So I tried to do something like this which seems nice too.

Answer 1

Solved! I was getting that error because to use StringComparer the element to sort in OrderBy() expression that element needs to be a string.

So when I know that element is a string I cast to a string and I use the RemoveDiacritics() method to ignore the accented letters and to look at them like non-accented.

public static IOrderedEnumerable<TSource> ToOrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
    if(!source.SafeAny())
        return null;

    return source.OrderBy(element => Utils.RemoveDiacritics(keySelector(element).ToString()));
}

To garantee the RemoveDiacritics() works fine I add a HtmlDecode() line.

public static string RemoveDiacritics(string text)
{
    if(text != null)
        text = WebUtility.HtmlDecode(text);

    string formD = text.Normalize(NormalizationForm.FormD);
    StringBuilder sb = new StringBuilder();

    foreach (char ch in formD)
    {
        UnicodeCategory uc = CharUnicodeInfo.GetUnicodeCategory(ch);
        if (uc != UnicodeCategory.NonSpacingMark)
        {
            sb.Append(ch);
        }
    }

    return sb.ToString().Normalize(NormalizationForm.FormC);
}