Array slice. A slice of an array is a range of elements. By using extension methods and generics, we simplify and clarify array slices.

Extension benefits. In the C# language, extension methods make for more reusable and powerful code. We write and test an array slice method.

Array

Input and output. Consider an array of integers. We wish to take a slice of a certain range of integers. The first argument is the start index, and the second is the last index (exclusive).

Slice(2, 5):

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Example. Here we see a generic method, which lets it act on any type. Our Slice method here uses this ability to simulate the built-in slice functionality of Python and other languages.

Extension

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        int[] a = new int[]
        {
            1,
            2,
            3,
            4,
            5,
            6,
            7
        };
        foreach (int i in a.Slice(0, 1))
        {
            Console.WriteLine(i);
        }
        Console.WriteLine();
        foreach (int i in a.Slice(0, 2))
        {
            Console.WriteLine(i);
        }
        Console.WriteLine();
        foreach (int i in a.Slice(2, 5))
        {
            Console.WriteLine(i);
        }
        Console.WriteLine();
        foreach (int i in a.Slice(2, -3))
        {
            Console.WriteLine(i);
        }
    }
}

public static class Extensions
{
    /// <summary>
    /// Get the array slice between the two indexes.
    /// ... Inclusive for start index, exclusive for end index.
    /// </summary>
    public static T[] Slice<T>(this T[] source, int start, int end)
    {
        // Handles negative ends.
        if (end < 0)
        {
            end = source.Length + end;
        }
        int len = end - start;

        // Return new array.
        T[] res = new T[len];
        for (int i = 0; i < len; i++)
        {
            res[i] = source[i + start];
        }
        return res;
    }
}
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Notes, generics. When T (or a similar letter) appears in brackets after a method name, this is a generic method. The letter is replaced with the type specified.

Generic

A discussion. How is this method different from LINQ Take and Skip? The method here can deal with negative parameters. And it may be faster because it doesn't use IEnumerable.

Take, TakeWhile

Skip, SkipWhile

String Slice

A summary. Here we saw a generic array slice method that is also an extension method. An extension method is appropriate as the method can be used throughout a project.