.NET method to convert a string to sentence case

Question

I'm looking for a function to convert a string of text that is in UpperCase to SentenceCase. All the examples I can find turn the text into TitleCase.

Sentence case in a general sense describes the way that capitalization is used within a sentence. Sentence case also describes the standard capitalization of an English sentence, i.e. the first letter of the sentence is capitalized, with the rest being lower case (unless requiring capitalization for a specific reason, e.g. proper nouns, acronyms, etc.).

Can anyone point me in the direction of a script or function for SentenceCase?

Answer 1

There isn't anything built in to .NET - however, this is one of those cases where regular expression processing actually may work well. I would start by first converting the entire string to lower case, and then, as a first approximation, you could use regex to find all sequences like [a-z]\.\s+(.), and use ToUpper() to convert the captured group to upper case. The RegEx class has an overloaded Replace() method which accepts a MatchEvaluator delegate, which allows you to define how to replace the matched value.

Here's a code example of this at work:

var sourcestring = "THIS IS A GROUP. OF CAPITALIZED. LETTERS.";
// start by converting entire string to lower case
var lowerCase = sourcestring.ToLower();
// matches the first sentence of a string, as well as subsequent sentences
var r = new Regex(@"(^[a-z])|\.\s+(.)", RegexOptions.ExplicitCapture);
// MatchEvaluator delegate defines replacement of setence starts to uppercase
var result = r.Replace(lowerCase, s => s.Value.ToUpper());

// result is: "This is a group. Of uncapitalized. Letters."

This could be refined in a number of different ways to better match a broader variety of sentence patterns (not just those ending in a letter+period).

Answer 2

A solution in F#:

open System

let proper (x : string) =
    x.Split(' ')
    |> Array.filter ((<>) "")
    |> Array.map (fun t ->
        let head = Seq.head t |> Char.ToUpper |> string
        let tail = Seq.tail t |> Seq.map (Char.ToLower >> string)
        Seq.append [head] tail
        |> Seq.reduce (fun acc elem -> acc + elem))
    |> Array.reduce (fun acc elem -> acc + " " + elem)

Answer 3

This is what I use (VB.NET). It works in most situations, including:

• multiple sentences
• sentences beginning and ending with spaces

• sentences beginning with characters other than A-Z. For example it will work for: "if you want $100.00 then just ask me".

  <Extension()>
  Public Function ToSentanceCase(ByVal s As String) As String
      ' Written by Jason. Inspired from: http://www.access-programmers.co.uk/forums/showthread.php?t=147680
  
      Dim SplitSentence() As String = s.Split(".")
  
      For i = 0 To SplitSentence.Count - 1
          Dim st = SplitSentence(i)
  
          If st.Trim = "" Or st.Trim.Count = 1 Then Continue For ' ignore empty sentences or sentences with only 1 character.
  
          ' skip past characters that are not A-Z, 0-9 (ASCII) at start of sentence.
          Dim y As Integer = 1
          Do Until y > st.Count
              If (Asc(Mid(st, y, 1)) >= 65 And Asc(Mid(st, y, 1)) <= 90) Or _
                    (Asc(Mid(st, y, 1)) >= 97 And Asc(Mid(st, y, 1)) <= 122) Or _
                   (Asc(Mid(st, y, 1)) >= 48 And Asc(Mid(st, y, 1)) <= 57) Then
                  GoTo Process
              Else
                  Dim w = Asc(Mid(st, y, 1))
                  y += 1
              End If
          Loop
          Continue For
  
  Process:
          Dim sStart As String = ""
          If y > 1 Then sStart = Left(st, 0 + (y - 1))
  
          Dim sMid As String = UCase(st(y - 1)) ' capitalise the first non-space character in sentence.
  
          Dim sEnd As String = Mid(st, y + 1, st.Length)
  
          SplitSentence(i) = sStart & sMid & sEnd
  
      Next
  
      ' rejoin sentances back together:
      Dim concat As String = ""
      For Each st As String In SplitSentence
          concat &= st & "."
      Next
  
      concat = concat.TrimEnd(1)
  
      Return concat
  
  End Function
  

But as for proper nouns and acronyms, well... there are always going to be situations in the English language where punctuation is not as simple. For example this script won't detect an ellipsis ("..."), or abbreviations (eg: "Mr. Jones lived on Magnolia Blvd. near Chris' house").

To address the problem completely you will need to produce a dictionary of all the possible abbreviations/punctuation's for the language, and keep the dictionary up-to-date! After considering this most will be happy with a compromise, otherwise just use Microsoft Word.

Answer 4

This works for me.

/// <summary>
/// Converts a string to sentence case.
/// </summary>
/// <param name="input">The string to convert.</param>
/// <returns>A string</returns>
public static string SentenceCase(string input)
{
    if (input.Length < 1)
        return input;

    string sentence = input.ToLower();
    return sentence[0].ToString().ToUpper() +
       sentence.Substring(1);
}

Answer 5

If your input string is not a sentence, but many sentences, this becomes a very difficult problem.

Regular expressions will prove an invaluable tool, but (1) you'll have to know them quite well to be effective, and (2) they might not be up to doing the job entirely on their own.

Consider this sentence

"Who's on 1st," Mr. Smith -- who wasn't laughing -- replied.

This sentence doesn't start with a letter, it has a digit, various punctuation, a proper name, and a . in the middle.

The complexities are enormous, and this is one sentence.

One of the most important things when using RegEx is to "know your data." If you know the breadth of types of sentences you'll be dealing with, your task will be more manageable.

In any event, you'll have to toy with your implementation until you are satisfied with your results. I suggest writing some automated tests with some sample input -- as you work on your implementation, you can run the tests regularly to see where you're getting close and where you're still missing the mark.

Answer 6

There is a built in ToTitleCase() function that will be extended to support multiple cultures in future.

Example from MSDN:

using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      string[] values = { "a tale of two cities", "gROWL to the rescue",
                          "inside the US government", "sports and MLB baseball",
                          "The Return of Sherlock Holmes", "UNICEF and children"};

      TextInfo ti = CultureInfo.CurrentCulture.TextInfo;
      foreach (var value in values)
         Console.WriteLine("{0} --> {1}", value, ti.ToTitleCase(value));
   }
}
// The example displays the following output:
//    a tale of two cities --> A Tale Of Two Cities
//    gROWL to the rescue --> Growl To The Rescue
//    inside the US government --> Inside The US Government
//    sports and MLB baseball --> Sports And MLB Baseball
//    The Return of Sherlock Holmes --> The Return Of Sherlock Holmes
//    UNICEF and children --> UNICEF And Children

While it is generally useful it has some important limitations:

Generally, title casing converts the first character of a word to uppercase and the rest of the characters to lowercase. However, this method does not currently provide proper casing to convert a word that is entirely uppercase, such as an acronym. The following table shows the way the method renders several strings.

...the ToTitleCase method provides an arbitrary casing behavior which is not necessarily linguistically correct. A linguistically correct solution would require additional rules, and the current algorithm is somewhat simpler and faster. We reserve the right to make this API slower in the future.

Source: http://msdn.microsoft.com/en-us/library/system.globalization.textinfo.totitlecase.aspx

Answer 7

If you'd like to sentence case a string containing punctuation other than just periods:

string input = "THIS IS YELLING! WHY ARE WE YELLING? BECAUSE WE CAN. THAT IS ALL.";
var sentenceRegex = new Regex(@"(^[a-z])|[?!.:,;]\s+(.)", RegexOptions.ExplicitCapture);
input = sentenceRegex.Replace(input.ToLower(), s => s.Value.ToUpper());

Answer 8

public string GetSentenceCase(string ReqdString) {
    string StrInSentCase = "";
    for (int j = 0; j < ReqdString.Length; j++) {
        if (j == 0) {
           StrInSentCase = ReqdString.ToString().Substring(j, 1).ToUpper();
        }
        else {
            StrInSentCase = StrInSentCase + ReqdString.ToString().Substring(j, 1).ToLower();
        }
    }
    return StrInSentCase.ToString();
}