Is there an easy way to return a string repeated X number of times?

Question

I'm trying to insert a certain number of indentations before a string based on an items depth and I'm wondering if there is a way to return a string repeated X times. Example:

string indent = "---";
Console.WriteLine(indent.Repeat(0)); //would print nothing.
Console.WriteLine(indent.Repeat(1)); //would print "---".
Console.WriteLine(indent.Repeat(2)); //would print "------".
Console.WriteLine(indent.Repeat(3)); //would print "---------".

Answer 1

If you only intend to repeat the same character you can use the string constructor that accepts a char and the number of times to repeat it new String(char c, int count).

For example, to repeat a dash five times:

string result = new String('-', 5);
Output: -----

Answer 2

If you're using .NET 4.0, you could use string.Concat together with Enumerable.Repeat.

int N = 5; // or whatever
Console.WriteLine(string.Concat(Enumerable.Repeat(indent, N)));

Otherwise I'd go with something like Adam's answer.

The reason I generally wouldn't advise using Andrey's answer is simply that the ToArray() call introduces superfluous overhead that is avoided with the StringBuilder approach suggested by Adam. That said, at least it works without requiring .NET 4.0; and it's quick and easy (and isn't going to kill you if efficiency isn't too much of a concern).

Answer 3

most performant solution for string

string result = new StringBuilder().Insert(0, "---", 5).ToString();

Answer 4

public static class StringExtensions
{
    public static string Repeat(this string input, int count)
    {
        if (!string.IsNullOrEmpty(input))
        {
            StringBuilder builder = new StringBuilder(input.Length * count);

            for(int i = 0; i < count; i++) builder.Append(input);

            return builder.ToString();
        }

        return string.Empty;
    }
}

Answer 5

For many scenarios, this is probably the neatest solution:

public static class StringExtensions
{
    public static string Repeat(this string s, int n)
        => new StringBuilder(s.Length * n).Insert(0, s, n).ToString();
}

Usage is then:

text = "Hello World! ".Repeat(5);

This builds on other answers (particularly @c0rd's). As well as simplicity, it has the following features, which not all the other techniques discussed share:

• Repetition of a string of any length, not just a character (as requested by the OP).
• Efficient use of StringBuilder through storage preallocation.

Answer 6

Use String.PadLeft, if your desired string contains only a single char.

public static string Indent(int count, char pad)
{
    return String.Empty.PadLeft(count, pad);
}

Credit due here

Answer 7

You can repeat your string (in case it's not a single char) and concat the result, like this:

String.Concat(Enumerable.Repeat("---", 5))

Answer 8

I would go for Dan Tao's answer, but if you're not using .NET 4.0 you can do something like that:

public static string Repeat(this string str, int count)
{
    return Enumerable.Repeat(str, count)
                     .Aggregate(
                        new StringBuilder(str.Length * count),
                        (sb, s) => sb.Append(s))
                     .ToString();
}

Answer 9

Works with strings and chars:

Strings and chars [version 1]

string.Join("", Enumerable.Repeat("text" , 2 ));    
//result: texttext

Strings [version 2]:

String.Concat(Enumerable.Repeat("text", 2));
//result: texttext

Strings and chars [version 3]

new StringBuilder().Insert(0, "text", 2).ToString(); 
//result: texttext

Chars only:

'5' * 3; 
//result: 555

---

Extension way:

(works FASTER - better for WEB)

public static class RepeatExtensions
{
    public static string Repeat(this string str, int times)
    {
        return (new StringBuilder()).Insert(0, str, times).ToString();
    }
}

usage:

 var a = "Hello".Repeat(3); 
 //result: HelloHelloHello

Answer 10

        string indent = "---";
        string n = string.Concat(Enumerable.Repeat(indent, 1).ToArray());
        string n = string.Concat(Enumerable.Repeat(indent, 2).ToArray());
        string n = string.Concat(Enumerable.Repeat(indent, 3).ToArray());

Answer 11

I like the answer given. Along the same lines though is what I've used in the past:

"".PadLeft(3*Indent,'-')

This will fulfill creating an indent but technically the question was to repeat a string. If the string indent is something like >-< then this as well as the accepted answer would not work. In this case, c0rd's solution using StringBuilder looks good, though the overhead of StringBuilder may in fact not make it the most performant. One option is to build an array of strings, fill it with indent strings, then concat that. To whit:

int Indent = 2;
        
string[] sarray = new string[6];  //assuming max of 6 levels of indent, 0 based

for (int iter = 0; iter < 6; iter++)
{
    //using c0rd's stringbuilder concept, insert ABC as the indent characters to demonstrate any string can be used
    sarray[iter] = new StringBuilder().Insert(0, "ABC", iter).ToString();
}

Console.WriteLine(sarray[Indent] +"blah");  //now pretend to output some indented line

We all love a clever solution but sometimes simple is best.

Answer 12

Another approach is to consider string as IEnumerable<char> and have a generic extension method which will multiply the items in a collection by the specified factor.

public static IEnumerable<T> Repeat<T>(this IEnumerable<T> source, int times)
{
    source = source.ToArray();
    return Enumerable.Range(0, times).SelectMany(_ => source);
}

So in your case:

string indent = "---";
var f = string.Concat(indent.Repeat(0)); //.NET 4 required
//or
var g = new string(indent.Repeat(5).ToArray());

Answer 13

Surprised nobody went old-school. I am not making any claims about this code, but just for fun:

public static string Repeat(this string @this, int count)
{
    var dest = new char[@this.Length * count];
    for (int i = 0; i < dest.Length; i += 1)
    {
        dest[i] = @this[i % @this.Length];
    }
    return new string(dest);
}

Answer 14

Not sure how this would perform, but it's an easy piece of code. (I have probably made it appear more complicated than it is.)

int indentCount = 3;
string indent = "---";
string stringToBeIndented = "Blah";
// Need dummy char NOT in stringToBeIndented - vertical tab, anyone?
char dummy = '\v';
stringToBeIndented.PadLeft(stringToBeIndented.Length + indentCount, dummy).Replace(dummy.ToString(), indent);

Alternatively, if you know the maximum number of levels you can expect, you could just declare an array and index into it. You would probably want to make this array static or a constant.

string[] indents = new string[4] { "", indent, indent.Replace("-", "--"), indent.Replace("-", "---"), indent.Replace("-", "----") };
output = indents[indentCount] + stringToBeIndented;      

Answer 15

I don't have enough rep to comment on Adam's answer, but the best way to do it imo is like this:

public static string RepeatString(string content, int numTimes) {
        if(!string.IsNullOrEmpty(content) && numTimes > 0) {
            StringBuilder builder = new StringBuilder(content.Length * numTimes);

            for(int i = 0; i < numTimes; i++) builder.Append(content);

            return builder.ToString();
        }

        return string.Empty;
    }

You must check to see if numTimes is greater then zero, otherwise you will get an exception.

Answer 16

Print a line with repetition.

Console.Write(new string('=', 30) + "\n");

==============================

Answer 17

For general use, solutions involving the StringBuilder class are best for repeating multi-character strings. It's optimized to handle the combination of large numbers of strings in a way that simple concatenation can't and that would be difficult or impossible to do more efficiently by hand. The StringBuilder solutions shown here use O(N) iterations to complete, a flat rate proportional to the number of times it is repeated.

However, for very large number of repeats, or where high levels of efficiency must be squeezed out of it, a better approach is to do something similar to StringBuilder's basic functionality but to produce additional copies from the destination, rather than from the original string, as below.

    public static string Repeat_CharArray_LogN(this string str, int times)
    {
        int limit = (int)Math.Log(times, 2);
        char[] buffer = new char[str.Length * times];
        int width = str.Length;
        Array.Copy(str.ToCharArray(), buffer, width);

        for (int index = 0; index < limit; index++)
        {
            Array.Copy(buffer, 0, buffer, width, width);
            width *= 2;
        }
        Array.Copy(buffer, 0, buffer, width, str.Length * times - width);

        return new string(buffer);
    }

This doubles the length of the source/destination string with each iteration, which saves the overhead of resetting counters each time it would go through the original string, instead smoothly reading through and copying the now much longer string, something that modern processors can do much more efficiently.

It uses a base-2 logarithm to find how many times it needs to double the length of the string and then proceeds to do so that many times. Since the remainder to be copied is now less than the total length it is copying from, it can then simply copy a subset of what it has already generated.

I have used the Array.Copy() method over the use of StringBuilder, as a copying of the content of the StringBuilder into itself would have the overhead of producing a new string with that content with each iteration. Array.Copy() avoids this, while still operating with an extremely high rate of efficiency.

This solution takes O(1 + log N) iterations to complete, a rate that increases logarithmically with the number of repeats (doubling the number of repeats equals one additional iteration), a substantial savings over the other methods, which increase proportionally.

Answer 18

Adding the Extension Method I am using all over my projects:

public static string Repeat(this string text, int count)
{
    if (!String.IsNullOrEmpty(text))
    {
        return String.Concat(Enumerable.Repeat(text, count));
    }
    return "";
}

Hope someone can take use of it...

Answer 19

I didn't see this solution. I find it simpler for where I currently am in software development:

public static void PrintFigure(int shapeSize)
{
    string figure = "\\/";
    for (int loopTwo = 1; loopTwo <= shapeSize - 1; loopTwo++)
    {
        Console.Write($"{figure}");
    }
}

Answer 20

You can create an ExtensionMethod to do that!

public static class StringExtension
{
  public static string Repeat(this string str, int count)
  {
    string ret = "";

    for (var x = 0; x < count; x++)
    {
      ret += str;
    }

    return ret;
  }
}

Or using @Dan Tao solution:

public static class StringExtension
{
  public static string Repeat(this string str, int count)
  {
    if (count == 0)
      return "";

    return string.Concat(Enumerable.Repeat(indent, N))
  }
}