How to shift the start of an array in C#?

Question

I'm trying to reorganize an array based on the first occurrence of a value (thus simulating similar functionality to a circular array.)

For example, in the following array I wish the first occurrence of the value 6 to become the new first element, and prior elements to become the latter:

So:

int[] myArray = {2, 3, 6, 1, 7, 6};

Becomes:

myArray = {6, 1, 7, 6, 2, 3};

What is the "best" way to achieve this?

Answer 1

int[] myArray = { 2, 3, 6, 1, 7, 6 };
myArray = myArray
            .SkipWhile(i => i != 6)
            .Concat(myArray.TakeWhile(i => i != 6))
            .ToArray();

Should do the trick!

You will need a using System.Linq;

Answer 2

Thorsten's solution creates a new array; here's an in place version which only creates a temporary array as large as the amount your rotation size:

public static void RotateLeft<T>(T[] array, int places)
{
    T[] temp = new T[places];
    Array.Copy(array, 0, temp, 0, places);
    Array.Copy(array, places, array, 0, array.Length - places);
    Array.Copy(temp, 0, array, array.Length - places, places);
}

I'm sure it could be done with just a single temporary buffer item, but it would be more complicated :)

As an efficiency measure, here's a "rotate left one place" shortcut:

public static void RotateLeft<T>(T[] array)
{
    T temp = array[0];
    Array.Copy(array, 0, array, 1, array.Length - 1);
    array[array.Length-1] = temp;
}

Answer 3

You could do the following:

1. Create new array of same size as original
2. Determine your "Start index"
3. Use Array.Copy() to copy everything from start index to end of source array to destination array
4. Use Array.Copy() to copy everything from 0 to start index of source array to the end of the destination array

That way you get a copy of your source array that looks as you expected.

You'll have to play with various overloads of Array.Copy(), however, because I don't know the exact parameter values right now.