Split a string with delimiters but keep the delimiters in the result in C#

Question

I would like to split a string with delimiters but keep the delimiters in the result.

How would I do this in C#?

Answer 1

If the split chars were , , . , and ; , I'd try:

using System.Text.RegularExpressions;
...    
string[] parts = Regex.Split(originalString, @"(?<=[.,;])")

(?<=PATTERN) is positive look-behind for PATTERN . It should match at any place where the preceding text fits PATTERN so there should be a match (and a split) after each occurrence of any of the characters.

Answer 2

If you want the delimiter to be its "own split", you can use Regex.Split eg:

string input = "plum-pear";
string pattern = "(-)";

string[] substrings = Regex.Split(input, pattern);    // Split on hyphens
foreach (string match in substrings)
{
   Console.WriteLine("'{0}'", match);
}
// The method writes the following to the console:
//    'plum'
//    '-'
//    'pear'

So if you are looking for splitting a mathematical formula, you can use the following Regex

@"([*()\^\/]|(?<!E)[\+\-])" 

This will ensure you can also use constants like 1E-02 and avoid having them split into 1E, - and 02

So:

Regex.Split("10E-02*x+sin(x)^2", @"([*()\^\/]|(?<!E)[\+\-])")

Yields:

• 10E-02
• *
• x
• +
• sin
• (
• x
• )
• ^
• 2

Answer 3

Building off from BFree's answer, I had the same goal, but I wanted to split on an array of characters similar to the original Split method, and I also have multiple splits per string:

public static IEnumerable<string> SplitAndKeep(this string s, char[] delims)
{
    int start = 0, index;

    while ((index = s.IndexOfAny(delims, start)) != -1)
    {
        if(index-start > 0)
            yield return s.Substring(start, index - start);
        yield return s.Substring(index, 1);
        start = index + 1;
    }

    if (start < s.Length)
    {
        yield return s.Substring(start);
    }
}

Answer 4

Just in case anyone wants this answer aswell...

Instead of string[] parts = Regex.Split(originalString, @"(?<=[.,;])") you could use string[] parts = Regex.Split(originalString, @"(?=yourmatch)") where yourmatch is whatever your separator is.

Supposing the original string was

777- cat

777 - dog

777 - mouse

777 - rat

777 - wolf

Regex.Split(originalString, @"(?=777)") would return

777 - cat

777 - dog

and so on

Answer 5

This version does not use LINQ or Regex and so it's probably relatively efficient. I think it might be easier to use than the Regex because you don't have to worry about escaping special delimiters. It returns an IList<string> which is more efficient than always converting to an array. It's an extension method, which is convenient. You can pass in the delimiters as either an array or as multiple parameters.

/// <summary>
/// Splits the given string into a list of substrings, while outputting the splitting
/// delimiters (each in its own string) as well. It's just like String.Split() except
/// the delimiters are preserved. No empty strings are output.</summary>
/// <param name="s">String to parse. Can be null or empty.</param>
/// <param name="delimiters">The delimiting characters. Can be an empty array.</param>
/// <returns></returns>
public static IList<string> SplitAndKeepDelimiters(this string s, params char[] delimiters)
{
    var parts = new List<string>();
    if (!string.IsNullOrEmpty(s))
    {
        int iFirst = 0;
        do
        {
            int iLast = s.IndexOfAny(delimiters, iFirst);
            if (iLast >= 0)
            {
                if (iLast > iFirst)
                    parts.Add(s.Substring(iFirst, iLast - iFirst)); //part before the delimiter
                parts.Add(new string(s[iLast], 1));//the delimiter
                iFirst = iLast + 1;
                continue;
            }

            //No delimiters were found, but at least one character remains. Add the rest and stop.
            parts.Add(s.Substring(iFirst, s.Length - iFirst));
            break;

        } while (iFirst < s.Length);
    }

    return parts;
}

Some unit tests:

text = "[a link|http://www.google.com]";
result = text.SplitAndKeepDelimiters('[', '|', ']');
Assert.IsTrue(result.Count == 5);
Assert.AreEqual(result[0], "[");
Assert.AreEqual(result[1], "a link");
Assert.AreEqual(result[2], "|");
Assert.AreEqual(result[3], "http://www.google.com");
Assert.AreEqual(result[4], "]");

Answer 6

A lot of answers to this! One I knocked up to split by various strings (the original answer caters for just characters ie length of 1). This hasn't been fully tested.

public static IEnumerable<string> SplitAndKeep(string s, params string[] delims)
{
    var rows = new List<string>() { s };
    foreach (string delim in delims)//delimiter counter
    {
        for (int i = 0; i < rows.Count; i++)//row counter
        {
            int index = rows[i].IndexOf(delim);
            if (index > -1
                && rows[i].Length > index + 1)
            {
                string leftPart = rows[i].Substring(0, index + delim.Length);
                string rightPart = rows[i].Substring(index + delim.Length);
                rows[i] = leftPart;
                rows.Insert(i + 1, rightPart);
            }
        }
    }
    return rows;
}

Answer 7

This seems to work, but its not been tested much.

public static string[] SplitAndKeepSeparators(string value, char[] separators, StringSplitOptions splitOptions)
{
    List<string> splitValues = new List<string>();
    int itemStart = 0;
    for (int pos = 0; pos < value.Length; pos++)
    {
        for (int sepIndex = 0; sepIndex < separators.Length; sepIndex++)
        {
            if (separators[sepIndex] == value[pos])
            {
                // add the section of string before the separator 
                // (unless its empty and we are discarding empty sections)
                if (itemStart != pos || splitOptions == StringSplitOptions.None)
                {
                    splitValues.Add(value.Substring(itemStart, pos - itemStart));
                }
                itemStart = pos + 1;

                // add the separator
                splitValues.Add(separators[sepIndex].ToString());
                break;
            }
        }
    }

    // add anything after the final separator 
    // (unless its empty and we are discarding empty sections)
    if (itemStart != value.Length || splitOptions == StringSplitOptions.None)
    {
        splitValues.Add(value.Substring(itemStart, value.Length - itemStart));
    }

    return splitValues.ToArray();
}

Answer 8

为避免向新行添加字符，请尝试以下操作：

 string[] substrings = Regex.Split(input,@"(?<=[-])");

Answer 9

我想说实现这一点的最简单方法（除了 Hans Kesting 提出的参数）是以常规方式拆分字符串，然后遍历数组并将分隔符添加到除最后一个元素之外的每个元素。

Answer 10

result = originalString.Split(separator);
for(int i = 0; i < result.Length - 1; i++)
    result[i] += separator;

( EDIT - this is a bad answer - I misread his question and didn't see that he was splitting by multiple characters.)

(EDIT - a correct LINQ version is awkward, since the separator shouldn't get concatenated onto the final string in the split array.)

Answer 11

Recently I wrote an extension method do to this:

public static class StringExtensions
    {
        public static IEnumerable<string> SplitAndKeep(this string s, string seperator)
        {
            string[] obj = s.Split(new string[] { seperator }, StringSplitOptions.None);

            for (int i = 0; i < obj.Length; i++)
            {
                string result = i == obj.Length - 1 ? obj[i] : obj[i] + seperator;
                yield return result;
            }
        }
    }

Answer 12

Iterate through the string character by character (which is what regex does anyway. When you find a splitter, then spin off a substring.

pseudo code

int hold, counter;
List<String> afterSplit;
string toSplit

for(hold = 0, counter = 0; counter < toSplit.Length; counter++)
{
   if(toSplit[counter] = /*split charaters*/)
   {
      afterSplit.Add(toSplit.Substring(hold, counter));
      hold = counter;
   }
}

That's sort of C# but not really. Obviously, choose the appropriate function names. Also, I think there might be an off-by-1 error in there.

But that will do what you're asking.

Answer 13

veggerby's answer modified to

• have no string items in the list
• have fixed string as delimiter like "ab" instead of single character

var delimiter = "ab";
var text = "ab33ab9ab"
var parts = Regex.Split(text, $@"({Regex.Escape(delimiter)})")
                 .Where(p => p != string.Empty)
                 .ToList();

// parts = "ab", "33", "ab", "9", "ab"

The Regex.Escape() is there just in case your delimiter contains characters which regex interprets as special pattern commands (like * , ( ) and thus have to be escaped.

Answer 14

I wanted to do a multiline string like this but needed to keep the line breaks so I did this

string x = 
@"line 1 {0}
line 2 {1}
";

foreach(var line in string.Format(x, "one", "two")
    .Split("\n") 
    .Select(x => x.Contains('\r') ? x + '\n' : x)
    .AsEnumerable()
) {
    Console.Write(line);
}

yields

line 1 one
line 2 two

Answer 15

I came across same problem but with multiple delimiters. Here's my solution:

    public static string[] SplitLeft(this string @this, char[] delimiters, int count)
    {
        var splits = new List<string>();
        int next = -1;
        while (splits.Count + 1 < count && (next = @this.IndexOfAny(delimiters, next + 1)) >= 0)
        {
            splits.Add(@this.Substring(0, next));
            @this = new string(@this.Skip(next).ToArray());
        }
        splits.Add(@this);
        return splits.ToArray();
    }

Sample with separating CamelCase variable names:

var variableSplit = variableName.SplitLeft(
    Enumerable.Range('A', 26).Select(i => (char)i).ToArray());

Answer 16

using System.Collections.Generic;
using System.Text.RegularExpressions;

namespace ConsoleApplication9
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = @"This;is:a.test";
            char sep0 = ';', sep1 = ':', sep2 = '.';
            string pattern = string.Format("[{0}{1}{2}]|[^{0}{1}{2}]+", sep0, sep1, sep2);
            Regex regex = new Regex(pattern);
            MatchCollection matches = regex.Matches(input);
            List<string> parts=new List<string>();
            foreach (Match match in matches)
            {
                parts.Add(match.ToString());
            }
        }
    }
}

Answer 17

I wrote this code to split and keep delimiters :

private static string[] SplitKeepDelimiters(string toSplit, char[] delimiters, StringSplitOptions splitOptions = StringSplitOptions.None)
{
    var tokens = new List<string>();
    int idx = 0;
    for (int i = 0; i < toSplit.Length; ++i)
    {
        if (delimiters.Contains(toSplit[i]))
        {
            tokens.Add(toSplit.Substring(idx, i - idx));  // token found
            tokens.Add(toSplit[i].ToString());            // delimiter
            idx = i + 1;                                  // start idx for the next token
        }
    }

    // last token
    tokens.Add(toSplit.Substring(idx));

    if (splitOptions == StringSplitOptions.RemoveEmptyEntries)
    {
        tokens = tokens.Where(token => token.Length > 0).ToList();
    }

    return tokens.ToArray();
}

Usage example:

string toSplit = "AAA,BBB,CCC;DD;,EE,";
char[] delimiters = new char[] {',', ';'};
string[] tokens = SplitKeepDelimiters(toSplit, delimiters, StringSplitOptions.RemoveEmptyEntries);
foreach (var token in tokens)
{
    Console.WriteLine(token);
}