Greek characters string to lower case

Question

i'm having some troubles transforming the string "SΨZΣ" to lower case.

In C# both .ToLower() and .ToLowerInvariant() gives me "sψzσ" as result. While javascript returns "sψzς".

After some research i think to have understood that the character 'Σ' should be translated to 'σ' only if it's not at the end of a word, in which case it should be turned into a 'ς' - so the javascript version is fine. And indeed i'm getting errors while calling an external API with the C# string, while the js string works fine.

Any idea on how i could make C# to lower the string correctly?

Luminance

Answer 1

Unfortunately there's no default way to do this in C#; At first when I looked at your question, I guessed that it may be something that setting the culture could fix, like:

string s = "SΨZΣ".ToLower(new CultureInfo("el-GR"));

but unfortunately this doesn't work. The problem is more complex, and therefore requires us to make our own solution:

    public string GreekToLower(string s)
    {
        string lowerString = s.ToLower();

        // Matches any 'σ' followed by whitespace or end of string
        string returnString = Regex.Replace(lowerString, "σ(\\s+|$)", "ς$1");
        return returnString;
    }

This lowercases your string, and then looks for any 'σ' character that is followed by one or more whitespace or occurs at the end of the string (the last word in your string likely won't be followed by whitespace) and then replaces it with 'ς', preserving any existing whitespace it finds.

Regex is probably best suited for these types of scenarios. I'm guessing that you'll probably also want to make sure that the greek diacritics are added or removed as well, like the tonos for words like Ρύθμιση --> ΡΥΘΜΙΣΗ. This can be done, but it's way more complex and will require a more heavy regular expression to evaluate all cases.

Voight

Probably better off looking for a word boundary, what about punctuation after the word (comma, full stop, etc) – Wagner

@Wagner true, but this will also catch characters such as apostrophes, hyphens, etc. Which could happen in the middle of the word. I'm not entirely sure of OP's desired behavior in that respect. – Voight

Answer 2

I am not familiar with the Greek alphabet but I would suggest implementing your own lower case method here is an example

char ToLowerCaseGreek(char letter) =>
return (char)(((int)letter) - ((int)'Α') - ((int)'α'));

First we calc the offset between the start of the upper case Greek alphabet (upper case alpha) to the start of the lower case of the Greek alphabet (lower case alpha) than we subtract that offset from our upper case Greek alphabet char to get the lower case char that matches it.

Yoakum

There's a few problems with your code; if you use the lambda expression operator, => this implies return and the compiler will complain if you use return after it. The second problem is it doesn't actually work as intended, giving the result of "螺ﱦ落ﱡ" when i input "SΨZΣ". – Voight