Replace a camel case string with a hyphenated string

Question

How would I change the string

aboutUs

To

about-us

I'd like to be able to do this with regex replace if possible. I've tried:

public static string ToHypenCase(this string source) {
    return Regex.Replace(source, @"[A-Z]", "-$1");
}

Answer 1

You can do it with a combination of regex and ToLower(), like this:

string s = "quickBrownFoxJumpsOverTheLazyDog";
string res = Regex.Replace(s, @"([a-z])([A-Z])", "$1-$2").ToLower();
Console.WriteLine(res);

Demo on ideone.

Answer 2

If you need fast solution with low allocation (it handles also @PeterL cases):

public static string ConvertFromCamelCaseToDashSyntax(string text)
{
    var buffer = ArrayPool<char>.Shared.Rent(text.Length + 10); // define max size of the internal buffer, 10 = max 10 segments

    try
    {      
        var resultLength = 0;
        for (var i = 0; i < text.Length; i++)
        {
            if (char.IsUpper(text[i]) && i > 0)
            {
                buffer[resultLength++] = '-';  
            }
            buffer[resultLength++] = char.ToLowerInvariant(text[i]);
        }

        return new string(buffer.AsSpan().Slice(0, resultLength));

    }
    finally
    {
        ArrayPool<char>.Shared.Return(buffer);
    }
}

Benchmark:

Method	Text	Mean	Error	StdDev	Ratio	Gen 0	Allocated
UsingRegex	quick(...)zyDog [32]	1,894.7 ns	2.38 ns	2.11 ns	1.00	0.0114	208 B
UsingArrayPoolAndSpans	quick(...)zyDog [32]	106.3 ns	0.23 ns	0.20 ns	0.06	0.0062	104 B