Subset of Array in C#

If I have an array with 12 elements and I want a new array with that drops the first and 12t开发者_JAVA百科h elements. For example, if my array looks like this:

__ __ __ __ __ __ __ __ __ __ __ __
a  b  c  d  e  f  g  h  i  j  k  l
__ __ __ __ __ __ __ __ __ __ __ __

I want to either transform it or create a new array that looks like

__ __ __ __ __ __ __ __ __ __

b  c  d  e  f  g  h  i  j  k 
__ __ __ __ __ __ __ __ __ __

I know I can do it by iterating over them. I was just wondering if there was a cleaner way built into C#.

**UPDATED TO FIX A TYPO. Changed 10 elements to 12 elements.

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LINQ is your friend. :)

var newArray = oldArray.Skip(1).Take(oldArray.Length - 2).ToArray();

Somewhat less efficient than manually creating the array and iterating over it of course, but far simple...

The slightly lengithier method that uses Array.Copy is the following.

var newArray = new int[oldArray.Count - 2];
Array.Copy(oldArray, 1, newArray, 0, newArray.Length);

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Linq is all nice and snazzy, but if you're looking for a 1-liner you could just throw together your own utility functions:

static class ArrayUtilities
{
    // create a subset from a range of indices
    public static T[] RangeSubset<T>(this T[] array, int startIndex, int length)
    {
        T[] subset = new T[length];
        Array.Copy(array, startIndex, subset, 0, length);
        return subset;
    }

    // create a subset from a specific list of indices
    public static T[] Subset<T>(this T[] array, params int[] indices)
    {
        T[] subset = new T[indices.Length];
        for (int i = 0; i < indices.Length; i++)
        {
            subset[i] = array[indices[i]];
        }
        return subset;
    }
}

So then you could do the following:

        char[] original = new char[] { 'a', 'b', 'c', 'd', 'e', 'f', 'g' };

        // array containing 'b' - 'f'
        char[] rangeSubset = original.RangeSubset(1, original.Length - 2);

        // array containing 'c', 'd', and 'f'
        char[] specificSubset = original.Subset(2, 3, 5);

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C# 8 has a Range and Index type

char[] a = { 'a', 'b', 'c',  'd',  'e',  'f',  'g',  'h',  'i',  'j',  'k',  'l' };
Index i1 = 1;  // number 1 from beginning
Index i2 = ^1; // number 1 from end
var slice = a[i1..i2]; // { 'b','c','d','e','f','g','h','i','j' }

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You can use ArraySegment<T> structure like below:

var arr = new[] { 1, 2, 3, 4, 5 };
var offset = 1;
var count = 2;
var subset = new ArraySegment<int>(arr, offset, count)
             .ToArray(); // output: { 2, 3 }

Check here for an extension method that makes use of it even easier.

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You can do this with Array.Copy or LINQ.

var letters = string[] { "a", "b", "c", "d", "e", "f", "g", "h", "i" };

int length = letters.Length - 2;
var items = new string[length];
Array.Copy(letters, 1, items, 0, length);
// or
var items = letters.Skip(1).Take(length).ToArray();

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Array.Copy() will do that for you, but you still have to create your new array with its correct size.

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string[] s = initialize the array...

var subset = s.Skip(1).Take(s.Length - 2).ToArray();

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If you want to avoid manually indexing the array. Don't try to pull request that anywhere though:

var newArray = oldArray.Skip(1).Reverse().Skip(1).Reverse().ToArray()

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Using the ReadOnlySpan struct the code of the substr for array may look like following:

var subArray = input.AsSpan(offset, length).ToArray();