How to copy part of an array to another array in C#?

Question

How can I copy a part of an array to another array?

Consider I'm having

int[] a = {1,2,3,4,5};

Now if I give the start index and end index of the array a it should get copied to another array.

Like if I give start index as 1 and end index as 3, the elements 2, 3, 4 should get copied in the new array.

score 304 · Accepted Answer · answered Apr 09 '09 at 07:52

304

int[] b = new int[3];
Array.Copy(a, 1, b, 0, 3);

a = source array
1 = start index in source array
b = destination array
0 = start index in destination array
3 = elements to copy

answered Apr 09 '09 at 07:52

Marc Gravell

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With named parameters that are available now, you would not need to document any of the 5 parameters. – Hamish Grubijan Aug 06 '12 at 16:47
12

@Hamish well, maybe. Personally I wouldn't add explicit names unless it made the code significantly clearer, and I'm not sure (in this case) that the parameter names *by themselves* would achieve that. – Marc Gravell Aug 06 '12 at 17:57

score 19 · Answer 2 · edited May 23 '17 at 12:18

19

See this question. LINQ Take() and Skip() are the most popular answers, as well as Array.CopyTo().

A purportedly faster extension method is described here.

edited May 23 '17 at 12:18

Community

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answered Apr 09 '09 at 07:55

Pontus Gagge

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Another question on SO with a suitable answer: http://stackoverflow.com/a/3539065/411428 – Manfred May 23 '13 at 12:03
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Note that LINQ is not ideal when dealing with performance-critical situations – XD face me Dec 27 '15 at 19:15

score 6 · Answer 3 · edited May 16 '17 at 10:55

6

int[] a = {1,2,3,4,5};

int [] b= new int[a.length]; //New Array and the size of a which is 4

Array.Copy(a,b,a.length);

Where Array is class having method Copy, which copies the element of a array to b array.

While copying from one array to another array, you have to provide same data type to another array of which you are copying.

edited May 16 '17 at 10:55

JJJ

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answered May 16 '17 at 10:01

bajran

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score 3 · Answer 4 · answered Apr 15 '22 at 22:32

3

In C# 8+ you can use ranges.

int a[] = {1,2,3,4,5};
int b[] = a[1..4]; // b = [2,3,4];

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/ranges

answered Apr 15 '22 at 22:32

JasonC

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score 1 · Answer 5 · answered Jan 09 '15 at 05:05

Note: I found this question looking for one of the steps in the answer to how to resize an existing array.

So I thought I would add that information here, in case anyone else was searching for how to do a ranged copy as a partial answer to the question of resizing an array.

For anyone else finding this question looking for the same thing I was, it is very simple:

Array.Resize<T>(ref arrayVariable, newSize);

where T is the type, i.e. where arrayVariable is declared:

T[] arrayVariable;

That method handles null checks, as well as newSize==oldSize having no effect, and of course silently handles the case where one of the arrays is longer than the other.

See the MSDN article for more.

score 0 · Answer 6 · answered Jan 26 '18 at 09:55

In case if you want to implement your own Array.Copy method.

Static method which is of generic type.

 static void MyCopy<T>(T[] sourceArray, long sourceIndex, T[] destinationArray, long destinationIndex, long copyNoOfElements)
 {
  long totaltraversal = sourceIndex + copyNoOfElements;
  long sourceArrayLength = sourceArray.Length;

  //to check all array's length and its indices properties before copying
  CheckBoundaries(sourceArray, sourceIndex, destinationArray, copyNoOfElements, sourceArrayLength);
   for (long i = sourceIndex; i < totaltraversal; i++)
     {
      destinationArray[destinationIndex++] = sourceArray[i]; 
     } 
  }

Boundary method implementation.

private static void CheckBoundaries<T>(T[] sourceArray, long sourceIndex, T[] destinationArray, long copyNoOfElements, long sourceArrayLength)
        {
            if (sourceIndex >= sourceArray.Length)
            {
                throw new IndexOutOfRangeException();
            }
            if (copyNoOfElements > sourceArrayLength)
            {
                throw new IndexOutOfRangeException();
            }
            if (destinationArray.Length < copyNoOfElements)
            {
                throw new IndexOutOfRangeException();
            }
        }

How to copy part of an array to another array in C#?

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