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c#arrays
Philip C
Philip C

Reputation: 1847

C# Changing the number of dimensions in an array

Is it possible, in C#, to convert a multi-dimensional array into a 1D array without having to copy all the elements from one to the other, something like:

int[,] x = new int[3,4];
int[] y = (int[])x;

This would allow the use of x as if it were a 12-element 1D array (and to return it from a function as such), but the compiler does not allow this conversion.

As far as I'm aware, a 2D array (or higher number of dimensions) is laid out in contiguous memory, so it doesn't seem impossible that it could work somehow. Using unsafe and fixed can allow access through a pointer, but this doesn't help with returning the array as 1D.

While I believe I can just use a 1D array throughout in the case I'm working on at present, it would be useful if this function was part of an adapter between something which returns a multidimensional array and something else which requires a 1D one.

Upvotes: 2

Views: 1103

Answers (6)

Felix K.
Felix K.

Reputation: 6281

You can't, it's not possible in C# to convert array's this way. You maybe could do it by using a external dll ( C/C++ ), but then you need to keep your array at a fixed location.

Speed

Generally i would advice to avoid using a 2D array because theese are slow in C#, better use jagged-array or even better single dimensionals with a little bit of math.

Int32[] myArray = new Int32[xSize * ySize];

// Access
myArray[x + (y * xSize)] = 5;

Upvotes: 2

Jamie Taylor
Jamie Taylor

Reputation: 1802

Riding on the back of Felix K.'s answer and quoting a fellow developer:

You can't convert a square to a line without losing information

Upvotes: 1

ionden
ionden

Reputation: 12786

You cannot cast, you'll have to copy the elements:

int[] y = (from int i in y select i).ToArray();

Upvotes: 0

Henk Holterman
Henk Holterman

Reputation: 273804

You can already iterate over a multidim as if it were a 1 dimensional array: 

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

  foreach (int i in data)
     ...  // i := 1 .. 5

And you could wrap a 1-dim array in a class and provide an indexer property this[int x1, int x2].

But everything else will require unsafe code or copying. Both will be inefficient.

Upvotes: 2

Biard Kévin
Biard Kévin

Reputation: 137

In C#, arrays cannot be resized dynamically. One approach is to use System.Collections.ArrayList instead of a native array. Another (faster) solution is to re-allocate the array with a different size and to copy the contents of the old array to the new array. The generic function resizeArray (below) can be used to do that.

One example here : 

// Reallocates an array with a new size, and copies the contents
// of the old array to the new array.
// Arguments:
//   oldArray  the old array, to be reallocated.
//   newSize   the new array size.
// Returns     A new array with the same contents.
public static System.Array ResizeArray (System.Array oldArray, int newSize) {
   int oldSize = oldArray.Length;
   System.Type elementType = oldArray.GetType().GetElementType();
   System.Array newArray = System.Array.CreateInstance(elementType,newSize);
   int preserveLength = System.Math.Min(oldSize,newSize);
   if (preserveLength > 0)
      System.Array.Copy (oldArray,newArray,preserveLength);
   return newArray; }

Upvotes: 2

PraveenVenu
PraveenVenu

Reputation: 8337

try

int[,] x = {{1, 2}, {2, 2}};
int[] y = new int[4];
System.Buffer.BlockCopy(x, 0, y, 0, 4);

Upvotes: 0

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