Shifting a String in C#

Question

  static void Main(string[] args)
  {
     string s = "ABCDEFGH";
     string newS = ShiftString(s);
     Console.WriteLine(newS);
  }
  public static string ShiftString(string t)
  {
     char[] c = t.ToCharArray();
     char save = c[0];
     for (int i = 0; i < c.Length; i++)
     {
        if (c[i] != c[0])
        c[i] = c[i - 1];
     }
     Console.WriteLine(c);
     String s = new string(c);
     return s;
  }

I need to shift the string s one space to the left, so i end up with the string: "BCDEFGHA" So i thought about changing the string into a char array and work my way from there, but im not sure how to succesfully make this work. I'm pretty certain i need a for loop, but i need some help on how to shift the char sequence one space to the left.

Answer 1

In C# 8 and above...

Rotate Right by one...

t = myString[^1] + myString[..^1];

Or, Rotate Left by one...

t = myString[1..] + myString[0];

Or, Rotate Right by an amount...

t = myString[^amount..] + myString[..^amount];

Or, Rotate Left by an amount...

t = myString[amount..] + myString[..amount];

Answer 2

Using Span<T> we can significantly improve the performance. E.g.:

public static class StringExtensions
{
    public static string ShiftString(this string s)
    {
        return string.Concat(s.AsSpan(1), s.AsSpan(0, 1));
    }
}

Benchmark

This answer + existing answers. Using spans, the shifting of the string becomes both faster and produces less garbage.

|  Method |     Data |     Mean |   Median | Allocated |
|-------- |--------- |---------:|---------:|----------:|
|    L33t | ABCDEFGH | 18.56 ns | 18.21 ns |      40 B |
|  Zs2020 | ABCDEFGH | 36.04 ns | 35.20 ns |      96 B |
| JohnWoo | ABCDEFGH | 47.69 ns | 47.39 ns |     104 B |
|  AlinaB | ABCDEFGH | 52.56 ns | 52.07 ns |     104 B |

Full test code

using System;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Configs;
using BenchmarkDotNet.Diagnosers;
using BenchmarkDotNet.Diagnostics.Windows;
using BenchmarkDotNet.Running;

namespace ConsoleApp10
{
    class Program
    {
        static void Main(string[] args)
        {
            var summary = BenchmarkRunner.Run<StringShiftTest>();
        }
    }

    [Config(typeof(Config))]
    public class StringShiftTest
    {
        private class Config : ManualConfig
        {
            public Config() => AddDiagnoser(MemoryDiagnoser.Default, new EtwProfiler());
        }

        [Params("ABCDEFGH")]
        public string Data;

        [Benchmark]
        public string L33t() => string.Concat(Data.AsSpan(1), Data.AsSpan(0, 1));

        [Benchmark]
        public string Zs2020() => (Data + Data).Substring(1, Data.Length);

        [Benchmark]
        public string JohnWoo() => Data.Substring(1, Data.Length - 1) + Data.Substring(0, 1);

        [Benchmark]
        public string AlinaB() => Data.Remove(0, 1) + Data.Substring(0, 1);
    }
}