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.

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.

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.

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.

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.