How can I convert text to Pascal case?

Question 1

First off, you are asking for title case and not camel-case, because in camel-case the first letter of the word is lowercase and your example shows you want the first letter to be uppercase.

At any rate, here is how you could achieve your desired result:

string textToChange = "WARD_VS_VITAL_SIGNS";
System.Text.StringBuilder resultBuilder = new System.Text.StringBuilder();

foreach(char c in textToChange)
{
    // Replace anything, but letters and digits, with space
    if(!Char.IsLetterOrDigit(c))
    {
        resultBuilder.Append(" ");
    }
    else 
    { 
        resultBuilder.Append(c); 
    }
}

string result = resultBuilder.ToString();

// Make result string all lowercase, because ToTitleCase does not change all uppercase correctly
result = result.ToLower();

// Creates a TextInfo based on the "en-US" culture.
TextInfo myTI = new CultureInfo("en-US",false).TextInfo;

result = myTI.ToTitleCase(result).Replace(" ", String.Empty);

Note: result is now WardVsVitalSigns.

If you did, in fact, want camel-case, then after all of the above, just use this helper function:

public string LowercaseFirst(string s)
{
    if (string.IsNullOrEmpty(s))
    {
        return string.Empty;
    }

    char[] a = s.ToCharArray();
    a[0] = char.ToLower(a[0]);

    return new string(a);
}

So you could call it, like this:

result = LowercaseFirst(result);

Question 2

You do not need a regular expression for that.

var yourString = "WARD_VS_VITAL_SIGNS".ToLower().Replace("_", " ");
TextInfo info = CultureInfo.CurrentCulture.TextInfo;
yourString = info.ToTitleCase(yourString).Replace(" ", string.Empty);
Console.WriteLine(yourString);

Question 3

Here is my quick LINQ & regex solution to save someone's time:

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

public string ToPascalCase(string original)
{
    Regex invalidCharsRgx = new Regex("[^_a-zA-Z0-9]");
    Regex whiteSpace = new Regex(@"(?<=\s)");
    Regex startsWithLowerCaseChar = new Regex("^[a-z]");
    Regex firstCharFollowedByUpperCasesOnly = new Regex("(?<=[A-Z])[A-Z0-9]+$");
    Regex lowerCaseNextToNumber = new Regex("(?<=[0-9])[a-z]");
    Regex upperCaseInside = new Regex("(?<=[A-Z])[A-Z]+?((?=[A-Z][a-z])|(?=[0-9]))");

    // replace white spaces with undescore, then replace all invalid chars with empty string
    var pascalCase = invalidCharsRgx.Replace(whiteSpace.Replace(original, "_"), string.Empty)
        // split by underscores
        .Split(new char[] { '_' }, StringSplitOptions.RemoveEmptyEntries)
        // set first letter to uppercase
        .Select(w => startsWithLowerCaseChar.Replace(w, m => m.Value.ToUpper()))
        // replace second and all following upper case letters to lower if there is no next lower (ABC -> Abc)
        .Select(w => firstCharFollowedByUpperCasesOnly.Replace(w, m => m.Value.ToLower()))
        // set upper case the first lower case following a number (Ab9cd -> Ab9Cd)
        .Select(w => lowerCaseNextToNumber.Replace(w, m => m.Value.ToUpper()))
        // lower second and next upper case letters except the last if it follows by any lower (ABcDEf -> AbcDef)
        .Select(w => upperCaseInside.Replace(w, m => m.Value.ToLower()));

    return string.Concat(pascalCase);
}

Example output:

"WARD_VS_VITAL_SIGNS"          "WardVsVitalSigns"
"Who am I?"                    "WhoAmI"
"I ate before you got here"    "IAteBeforeYouGotHere"
"Hello|Who|Am|I?"              "HelloWhoAmI"
"Live long and prosper"        "LiveLongAndProsper"
"Lorem ipsum dolor..."         "LoremIpsumDolor"
"CoolSP"                       "CoolSp"
"AB9CD"                        "Ab9Cd"
"CCCTrigger"                   "CccTrigger"
"CIRC"                         "Circ"
"ID_SOME"                      "IdSome"
"ID_SomeOther"                 "IdSomeOther"
"ID_SOMEOther"                 "IdSomeOther"
"CCC_SOME_2Phases"             "CccSome2Phases"
"AlreadyGoodPascalCase"        "AlreadyGoodPascalCase"
"999 999 99 9 "                "999999999"
"1 2 3 "                       "123"
"1 AB cd EFDDD 8"              "1AbCdEfddd8"
"INVALID VALUE AND _2THINGS"   "InvalidValueAnd2Things"

Question 4

Single semicolon solution:

public static string PascalCase(this string word)
{
    return string.Join("" , word.Split('_')
                 .Select(w => w.Trim())
                 .Where(w => w.Length > 0)
                 .Select(w => w.Substring(0,1).ToUpper() + w.Substring(1).ToLower()));
}

Question 5

Extension method for System.String with .NET Core compatible code by using System and System.Linq.

Does not modify the original string.

.NET Fiddle for the code below

using System;
using System.Linq;

public static class StringExtensions
{
    /// <summary>
    /// Converts a string to PascalCase
    /// </summary>
    /// <param name="str">String to convert</param>

    public static string ToPascalCase(this string str){

        // Replace all non-letter and non-digits with an underscore and lowercase the rest.
        string sample = string.Join("", str?.Select(c => Char.IsLetterOrDigit(c) ? c.ToString().ToLower() : "_").ToArray());

        // Split the resulting string by underscore
        // Select first character, uppercase it and concatenate with the rest of the string
        var arr = sample?
            .Split(new []{'_'}, StringSplitOptions.RemoveEmptyEntries)
            .Select(s => $"{s.Substring(0, 1).ToUpper()}{s.Substring(1)}");

        // Join the resulting collection
        sample = string.Join("", arr);

        return sample;
    }
}

public class Program
{
    public static void Main()
    {
        Console.WriteLine("WARD_VS_VITAL_SIGNS".ToPascalCase()); // WardVsVitalSigns
        Console.WriteLine("Who am I?".ToPascalCase()); // WhoAmI
        Console.WriteLine("I ate before you got here".ToPascalCase()); // IAteBeforeYouGotHere
        Console.WriteLine("Hello|Who|Am|I?".ToPascalCase()); // HelloWhoAmI
        Console.WriteLine("Live long and prosper".ToPascalCase()); // LiveLongAndProsper
        Console.WriteLine("Lorem ipsum dolor sit amet, consectetur adipiscing elit.".ToPascalCase()); // LoremIpsumDolorSitAmetConsecteturAdipiscingElit
    }
}

Question 6

var xs = "WARD_VS_VITAL_SIGNS".Split('_');

var q =

    from x in xs

    let first_char = char.ToUpper(x[0]) 
    let rest_chars = new string(x.Skip(1).Select(c => char.ToLower(c)).ToArray())

    select first_char + rest_chars;

Question 7

Some answers are correct but I really don't understand why they set the text to LowerCase first, because the ToTitleCase will handle that automatically:

var text = "WARD_VS_VITAL_SIGNS".Replace("_", " ");

TextInfo textInfo = CultureInfo.CurrentCulture.TextInfo;
text = textInfo.ToTitleCase(text).Replace(" ", string.Empty);

Console.WriteLine(text);

Question 8

You can use this:

public static string ConvertToPascal(string underScoreString)
    {
        string[] words = underScoreString.Split('_');

        StringBuilder returnStr = new StringBuilder();

        foreach (string wrd in words)
        {
            returnStr.Append(wrd.Substring(0, 1).ToUpper());
            returnStr.Append(wrd.Substring(1).ToLower());

        }
        return returnStr.ToString();
    }

Question 9

This answer understands that there are Unicode categories which can be tapped while processing the text to ignore the connecting characters such as - or _. In regex parlance it is \p (for category) then the type which is {Pc} for punctuation and connector type character; \p{Pc} using our MatchEvaluator which is kicked off for each match within a session.

So during the match phase, we get words and ignore the punctuations, so the replace operation handles the removal of the connector character. Once we have the match word, we can push it down to lowercase and then only up case the first character as the return for the replace:

public static class StringExtensions
{
    public static string ToPascalCase(this string initial)
        => Regex.Replace(initial, 
                       // (Match any non punctuation) & then ignore any punctuation
                         @"([^\p{Pc}]+)[\p{Pc}]*", 
                         new MatchEvaluator(mtch =>
        {
            var word = mtch.Groups[1].Value.ToLower();

            return $"{Char.ToUpper(word[0])}{word.Substring(1)}";
        }));
}

Usage:

"TOO_MUCH_BABY".ToPascalCase(); // TooMuchBaby
"HELLO|ITS|ME".ToPascalCase();  // HelloItsMe

See Word Character in Character Classes in Regular Expressions

Pc Punctuation, Connector. This category includes ten characters, the most commonly used of which is the LOWLINE character (_), u+005F.

Question 10

If you did want to replace any formatted string into a pascal case then you can do

    public static string ToPascalCase(this string original)
    {
        string newString = string.Empty;
        bool makeNextCharacterUpper = false;
        for (int index = 0; index < original.Length; index++)
        {
            char c = original[index];
            if(index == 0)
                newString += $"{char.ToUpper(c)}";
            else if (makeNextCharacterUpper)
            {
                newString += $"{char.ToUpper(c)}";
                makeNextCharacterUpper = false;
            }
            else if (char.IsUpper(c))
                newString += $" {c}";
            else if (char.IsLower(c) || char.IsNumber(c))
                newString += c;
            else if (char.IsNumber(c))
                newString += $"{c}";
            else
            {
                makeNextCharacterUpper = true;   
                newString += ' ';
            }
        }

        return newString.TrimStart().Replace(" ", "");
    }

Tested with strings I|Can|Get|A|String ICan_GetAString i-can-get-a-string i_can_get_a_string I Can Get A String ICanGetAString

Question 11

I found this gist useful after adding a ToLower() to it.

"WARD_VS_VITAL_SIGNS".ToLower().Split(new [] {"_"}, StringSplitOptions.RemoveEmptyEntries).Select(s => char.ToUpperInvariant(s[0]) + s.Substring(1, s.Length - 1)).Aggregate(string.Empty, (s1, s2) => s1 + s2)