跳过x个字符，然后在c＃中为每个y个字符插入一个字符串

Question

Given a sting, how can I skip the first x characters and then insert a value for every y characters?

For example:

“Lorem ipsum dolor sit amet,” 

when skipping the first 10 caracters and then indsert “[here]” for every 3 caracters becomes:

“Lorem ipsu[here]m d[here]olo[here]r s[here]it [here]ame[here]t,”

What is the most efficient, fastest way of doing this in C#?

My current function looks like this but isn't doing the skipping part, I know how to implement the skipping part but the technique used does not seem to be optimal:

public static string InsertHere(string source)
    {
        if (string.IsNullOrWhiteSpace(source))
        {
            return string.Empty;
        }

        int count = 0;
        var sb = new StringBuilder();
        foreach (char c in source)
        {
            count++;
            sb.Append(c);
            if (count == 10)
            {
                count = 0;
                sb.Append(@"[here]");
            }
        }
        return sb.ToString();
    }

Answer 1

Not sure if it's faster (you really need to benchmark this):

static Regex Rx = new Regex("(^.{10}|.{3})", RegexOptions.Compiled);

//...
var result = Rx.Replace(input, "$0[here]");

Using a static compiled regex for best speed in a regex solution.

Answer 2

You'd have to profile them to see what's best, but here's my effort, I've gone for a string reader into a buffer approach.

    public static string InsertStringRepeatedly(string source, int skip, int insertEvery, string toInsert)
    {
        var sb = new StringBuilder();
        using (var sr = new StringReader(source))
        {
            var buffer = new char[Math.Max(skip, insertEvery)];
            var read = sr.Read(buffer, 0, skip);
            sb.Append(buffer, 0, read);
            while (sr.Peek() > 0)
            {
                sb.Append(toInsert);
                read = sr.Read(buffer, 0, insertEvery);
                sb.Append(buffer, 0, read);
            }
        }
        return sb.ToString();
    }

Edit:

Fixed for edge cases source.Length < 10 or not whole multiple of 10 + 3*x. Also use just one buffer now.

Usage example:

    private static void Main(string[] args)
    {
        var result = InsertStringRepeatedly("Lorem ipsum dolor sit amet,", 10, 3, "[Here]");
        Console.Write("\"");
        Console.Write(result);
        Console.WriteLine("\""); //quotes to show we dealt with edge cases correctly
        Console.ReadLine();
    }

Answer 3

No need to Regex . Try String methods for more performance:

string str = "Lorem ipsum dolor sit amet,";
var rep = "[here]";

var step = 10 + rep.Length;
while (str.Length > step)
{
    str = str.Insert(step, rep);
    step = step + 3 + rep.Length;
}

Answer 4

I thought I might as well put my modifications into an answer.

I should stress that this may well not be the best way to do it but it is the simplest modification of your code to do it and definitely works...

public static string InsertHere(string source, int skip, int repeatPeriod)
{
    if (string.IsNullOrWhiteSpace(source))
    {
        return string.Empty;
    }

    int count = -1*(skip-repeatPeriod);
    var sb = new StringBuilder();
    foreach (char c in source)
    {
        count++;
        sb.Append(c);
        if (count == repeatPeriod)
        {
            count = 0;
            sb.Append(@"[here]");
        }
    }
    return sb.ToString();
}

Answer 5

I'm not very proficient with C# yet (I have a VB background), but the first thing that comes to mind is this:

 string WordProcess(string StringToProcess, string InsertValue, byte NumberToProcess )
    {
        string Result = "";
        while (StringToProcess != "")
        {
            for (byte b = 0; b < NumberToProcess; b++)
            {
                string TempString = StringToProcess;
                Result += TempString.Remove(1, TempString.Length - 1);
                StringToProcess = StringToProcess.Remove(0, 1);
            }
            Result += InsertValue;
        }
        return Result;
    }

I've tried it and it seemed to work fine for me, so you should be able to just copy and paste it in and use it as it is. Not sure how fast it is, but it works at least.

I hope you find this useful/helpful.