C# Remove, Trim Punctuation

Remove, trim punctuation.

The Trim method has limitations. It can handle groups of characters, but these must be specified explicitly. A requirement is to remove punctuation from the starts and ends of strings. With a custom method we avoid the complexity of Trim.

Trim

Example. In this example we introduce a method called TrimPunctuation. It contains two loops. Each of these loops uses the char.IsPunctuation method. When a non-punctuation character is encountered, they stop iterating, with the break keyword.

char.IsPunctuationBreak

First loop: This counts the number of punctuation characters at the start of the string.

Second loop: This loop counts the punctuation at the end. It iterates in the reverse order.

If no punctuation was found, the method returns the original string unchanged. If all characters were punctuation, it returns an empty string. And it returns a substring with the punctuation characters removed in the final case.

Empty StringSubstring

C# program that trims punctuation characters

using System;

class Program
{
    static void Main()
    {
	string[] array =
	{
	    "Do you like this site?",
	    "--cool--",
	    "...ok!",
	    "None",
	    ""
	};
	// Call method on each string.
	foreach (string value in array)
	{
	    Console.WriteLine(Program.TrimPunctuation(value));
	}
    }

    /// &llt;summary>
    /// TrimPunctuation from start and end of string.
    /// </summary>
    static string TrimPunctuation(string value)
    {
	// Count start punctuation.
	int removeFromStart = 0;
	for (int i = 0; i < value.Length; i++)
	{
	    if (char.IsPunctuation(value[i]))
	    {
		removeFromStart++;
	    }
	    else
	    {
		break;
	    }
	}

	// Count end punctuation.
	int removeFromEnd = 0;
	for (int i = value.Length - 1; i >= 0; i--)
	{
	    if (char.IsPunctuation(value[i]))
	    {
		removeFromEnd++;
	    }
	    else
	    {
		break;
	    }
	}
	// No characters were punctuation.
	if (removeFromStart == 0 &&
	    removeFromEnd == 0)
	{
	    return value;
	}
	// All characters were punctuation.
	if (removeFromStart == value.Length &&
	    removeFromEnd == value.Length)
	{
	    return "";
	}
	// Substring.
	return value.Substring(removeFromStart,
	    value.Length - removeFromEnd - removeFromStart);
    }
}

Output

Do you like this site
cool
ok
None

Regex. The string manipulation here could be done with Regex. And the code would even be shorter. It would also be slower. This is not a big consideration for most programs. But for important programs, performance is often more concerning.

Regex.Match

Discussion. Much of computer programming involves string manipulation. This method could be useful for handling the forms at the back-end of a website. It could help with handling invalid fields in a database.

Also: If you have a specific requirement, such as removing all punctuation and also all numbers, this sort of solution can come in handy.

Note: A regex could still be used, but it will become comparatively more complex.

Summary. Some of the .NET Framework methods have serious limitations. They are useful for a narrow purpose, but if your requirements exceed this, you have a problem. But any framework that has every possible method in it would be unwieldy.

Review: We developed a simple looping method that strips leading and trailing punctuation from a string.

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