Split string and keeping the delimiter without Regex C#

Question

Problem: spending too much time solving simple problems. Oh, here's the simple problem.

• Input: string inStr, char delimiter
• Output: string[] outStrs where string.Join("", outStrs) == inStr and each item in outStrs before the last item must end with the delimiter. If inStr ends with the delimiter, then the last item in outStrs ends with the delimiter as well.

Example 1:

• Input: "my,string,separated,by,commas", ','
• Output: ["my,", "string,", "separated,", "by,", "commas"]

Example 2:

• Input: "my,string,separated,by,commas,", ','
• Output: ["my,", "string,", "separated,", "by,", "commas,"] (notice trailing comma)

Solution with Regex: here

I want to avoid using Regex, simply because this requires only character comparison. It's algorithmically just as complex to do as what string.Split() does. It bothers me that I cannot find a more succinct way to do what I want.

My bad solution, which doesn't work for me... it should be faster and more succinct.

var outStr = inStr.Split(new[]{delimiter}, 
                         StringSplitOptions.RemoveEmptyEntries)
                  .Select(x => x + delimiter).ToArray();
if (inStr.Last() != delimiter) {
    var lastOutStr = outStr.Last();
    outStr[outStr.Length-1] = lastOutStr.Substring(0, lastOutStr.Length-1);
}

Answer 1

public static IEnumerable<string> SplitAndKeep(this string s, string[] delims)
    {
        int start = 0, index;
        string selectedSeperator = null;
        while ((index = s.IndexOfAny(delims, start, out selectedSeperator)) != -1)
        {
            if (selectedSeperator == null)
                continue;
            if (index - start > 0)
                yield return s.Substring(start, index - start);
            yield return s.Substring(index, selectedSeperator.Length);
            start = index + selectedSeperator.Length;
        }

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

Answer 2

Using LINQ:

string input = "my,string,separated,by,commas";
string[] groups = input.Split(',');
string[] output = groups
    .Select((x, idx) => x + (idx < groups.Length - 1 ? "," : string.Empty))
    .Where(x => x != "")
    .ToArray();

Split the string into groups, then transform every group that is not the last element by appending a comma to it.

Just thought of another way you could do it, but I don't think this method is as clear:

string[] output = (input + ',').Split( new[] { "," }, StringSplitOptions.RemoveEmptyEntries)
    .Select(x => x + ',').ToArray();

Answer 3

Seems pretty simple to me without using Regex:

string inStr = "dasdasdas";
char delimiter = 'A';
string[] result = inStr.Split(new string[] { inStr }, System.StringSplitOptions.RemoveEmptyEntries);
string lastItem = result[result.Length - 1];
int amountOfLoops = lastItem[lastItem.Length - 1] == delimiter ? result.Length - 1 : result.Length - 2;
for (int i = 0; i < amountOfLoops; i++)
{
    result[i] += delimiter;
}