ToCamelCase

Converts a string to camel case.

• Use Regex.Matches() with an appropriate regular expression to break the string into words.
• Use string.Join() and string.ToLower() to convert the words to lowercase and combine them adding as a separator.
• Use CultureInfo.TextInfo.ToTitleCase() on the result to convert it to title case, string.Replace() with a regular expression to remove spaces afterwards.
• Finally, use IEnumerable.Select() on the result to convert the first character to lowercase and return a string from the result.

using System.Globalization;
using System.Text.RegularExpressions;
using System.Linq;

public static partial class _30s 
{
  public static string ToCamelCase(string str) 
  {
    Regex pattern = new Regex(@"[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+");
    return new string(
      new CultureInfo("en-US", false)
        .TextInfo
        .ToTitleCase(
          string.Join(" ", pattern.Matches(str)).ToLower()
        )
        .Replace(@" ", "")
        .Select((x, i) => i == 0 ? char.ToLower(x) : x)
        .ToArray()
    );
  }
}

_30s.ToCamelCase("some_database_field_name"); // "someDatabaseFieldName"
_30s.ToCamelCase("Some label that needs to be title-cased"); // "someLabelThatNeedsToBeCamelized"
_30s.ToCamelCase("some-package-name"); // "somePackageName"
_30s.ToCamelCase("some-mixed_string with spaces_underscores-and-hyphens"); // "someMixedStringWithSpacesUnderscoresAndHyphens"