Array slices in C#

Question

How do you do it? Given a byte array:

byte[] foo = new byte[4096];

How would I get the first x bytes of the array as a separate array? (Specifically, I need it as an IEnumerable<byte>)

This is for working with Sockets. I figure the easiest way would be array slicing, similar to Perls syntax:

@bar = @foo[0..40];

Which would return the first 41 elements into the @bar array. Is there something in C# that I'm just missing, or is there some other thing I should be doing?

LINQ is an option for me (.NET 3.5), if that helps any.

Answer 1

You could use the arrays CopyTo() method...

EDIT: Or with LINQ you can use Skip() and Take()...

EDIT2: Usage of LINQ Skip and Take:

byte[] arr = {1, 2, 3, 4, 5, 6, 7, 8};
var subset = arr.Skip(2).Take(2);

Answer 2

I do not think C# supports the Range semantics you could write an Extension method though like...

public static IEnumerator<Byte> Range(this byte[] array, int start, int end);

But like others have said if you do not need to set a start index then Take is all you need.

Answer 3

If you want IEnumerable<byte>, then just

IEnumerable<byte> data = foo.Take(x);

Answer 4

You can use Take extension method

var array = new byte[] {1, 2, 3, 4};
var firstTwoItems = array.Take(2);

Answer 5

Arrays are enumerable, so your foo already is an IEnumerable<byte> itself. Simply use LINQ sequence methods like Take() to get what you want out of it:

byte[] foo = new byte[4096];

var bar = foo.Take(41);

If you really need an array from any IEnumerable<byte> value, you could use the ToArray() method for that. Here that does not seem to be the case.

Answer 6

You could use a wrapper around the original array (which is IList), like in this (untested) piece of code.

public class SubList<T> : IList<T>
{
    #region Fields

private readonly int startIndex;
private readonly int endIndex;
private readonly int count;
private readonly IList<T> source;

#endregion

public SubList(IList<T> source, int startIndex, int count)
{
    this.source = source;
    this.startIndex = startIndex;
    this.count = count;
    this.endIndex = this.startIndex + this.count - 1;
}

#region IList<T> Members

public int IndexOf(T item)
{
    if (item != null)
    {
        for (int i = this.startIndex; i <= this.endIndex; i++)
        {
            if (item.Equals(this.source[i]))
                return i;
        }
    }
    else
    {
        for (int i = this.startIndex; i <= this.endIndex; i++)
        {
            if (this.source[i] == null)
                return i;
        }
    }
    return -1;
}

public void Insert(int index, T item)
{
    throw new NotSupportedException();
}

public void RemoveAt(int index)
{
    throw new NotSupportedException();
}

public T this[int index]
{
    get
    {
        if (index >= 0 && index < this.count)
            return this.source[index + this.startIndex];
        else
            throw new IndexOutOfRangeException("index");
    }
    set
    {
        if (index >= 0 && index < this.count)
            this.source[index + this.startIndex] = value;
        else
            throw new IndexOutOfRangeException("index");
    }
}

#endregion

#region ICollection<T> Members

public void Add(T item)
{
    throw new NotSupportedException();
}

public void Clear()
{
    throw new NotSupportedException();
}

public bool Contains(T item)
{
    return this.IndexOf(item) >= 0;
}

public void CopyTo(T[] array, int arrayIndex)
{
    for (int i=0; i<this.count; i++)
    {
        array[arrayIndex + i] = this.source[i + this.startIndex];
    }
}

public int Count
{
    get { return this.count; }
}

public bool IsReadOnly
{
    get { return true; }
}

public bool Remove(T item)
{
    throw new NotSupportedException();
}

#endregion

#region IEnumerable<T> Members

public IEnumerator<T> GetEnumerator()
{
    for (int i = this.startIndex; i < this.endIndex; i++)
    {
        yield return this.source[i];
    }
}

#endregion

#region IEnumerable Members

IEnumerator IEnumerable.GetEnumerator()
{
    return GetEnumerator();
}

#endregion

}

Answer 7

int slicelength = 41;
int startoffset = 0;
byte[] foo = new byte[4096];
byte[] destfoo = new byte[slicelength];
Array.Copy(foo, startoffset, destfoo, 0, slicelength);

Answer 8

You could use ArraySegment<T>. It's very light-weight as it doesn't copy the array:

string[] a = { "one", "two", "three", "four", "five" };
var segment = new ArraySegment<string>( a, 1, 2 );

Answer 9

Another possibility I haven't seen mentioned here: Buffer.BlockCopy() is slightly faster than Array.Copy(), and it has the added benefit of being able to convert on-the-fly from an array of primitives (say, short[]) to an array of bytes, which can be handy when you've got numeric arrays that you need to transmit over Sockets.

Answer 10

byte[] foo = new byte[4096];

byte[] bar = foo.Take(40).ToArray();