using System;

using System.Collections.Generic;

using System.Linq;

namespace NumSharp.Utilities

{

public static class SteppingExtension

{

// this will step an array ... [1,2,3,4].Step(2) => [1,3]

// if step is 1 the original array is returned without copying it

public static T[] Step<T>(this T[] array, int step)

{

// todo: optimize performance? avoid array copying as much as possible, etc.

if (step == 0)

throw new ArgumentException("Step of 0 is not allowed!");

if (step == 1)

return array;

if (step == -1)

return array.Reverse().ToArray();

var stepped_enumerable = Step(step < 0 ? array.Reverse().GetEnumerator() : array.OfType<T>().GetEnumerator(), Math.Abs(step));

return stepped_enumerable.ToArray();

}

private static IEnumerable<T> Step<T>(IEnumerator<T> enumerator, int step)

{

while (enumerator.MoveNext())

{

yield return enumerator.Current;

for (int i = 0; i < step - 1; i++)

{

if (!enumerator.MoveNext())

yield break;

}

}

}

}

}