c# assign 1 dimensional array to 2 dimensional array syntax

Question

I want to do something like:

object[] rowOfObjects = GetRow();//filled somewhere else
object[,] tableOfObjects = new object[10,10];

tableOfObjects[0] = rowOfObjects;

is this somehow possible and what is the syntax?

or I need to do this:

for (int i = 0; i < rowOfObjects.Length; i++)
{
   tableOfObjects[0,i] = rowOfObjects[i];
}

and fill up the 2 dimensional arrays row using a loop?

Thanks

Matthew Finlay · Accepted Answer · 2016-07-08 00:01:38Z

12

If your array is an array of value types, it is possible.

int[,] twoD = new int[2, 2] {
    {0,1},
    {2,3}
};
int[] oneD = new int[2] 
    { 4, 5 };
int destRow = 1;
Buffer.BlockCopy(
    oneD, // src
    0, // srcOffset
    twoD, // dst
    destRow * twoD.GetLength(1) * sizeof(int), // dstOffset
    oneD.Length * sizeof(int)); // count
// twoD now equals
// {0,1},
// {4,5}

It is not possible with an array of objects.

Note: Since .net3.5 this will only work with an array of primitives.

edited Jul 8, 2016 at 0:01

answered Oct 3, 2011 at 0:59

Matthew Finlay

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Comments

Guffa · Accepted Answer · 2009-07-08 16:52:24Z

11

No, if you are using a two dimensional array it's not possible. You have to copy each item.

If you use a jagged array, it works just fine:

// create array of arrays
object[][] tableOfObject = new object[10][];
// create arrays to put in the array of arrays
for (int i = 0; i < 10; i++) tableOfObject[i] = new object[10];

// get row as array
object[] rowOfObject = GetRow();
// put array in array of arrays
tableOfObjects[0] = rowOfObjects;

If you are getting all the data as rows, you of course don't need the loop that puts arrays in the array of arrays, as you would just replace them anyway.

answered Jul 8, 2009 at 16:52

Guffa

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5 Comments

m3ntat Over a year ago

Thanks so what is the difference between: object[][] tableOfObject = new object[10][10]; and object[,] tableOfObjects = new object[10,10]; Many thanks.

Guffa Over a year ago

An object[,] is a two dimensional array, it is always rectangular (all rows are the same length). An object[][] is a jagged array; an array of object[] arrays. As each row is an array in itself, they don't have to be the same length.

Blindy Over a year ago

Keep in mind that jagged arrays have poorer performance and occupy more memory than "2d arrays" (they're actually held in memory as a 1d array). Depending on what your program does, this may matter.

Ed Swangren Over a year ago

@Blindy: You have that completely backward. Jagged arrays perform better than 2D arrays. Not sure who told you that, but it isn't true. Here is a good write up on the topic

Ed Swangren Over a year ago

@Blindy: Even better: stackoverflow.com/questions/468832/…

roxton · Accepted Answer · 2025-05-05 15:30:46Z

In .NET Core 2.1 and later, you can use MemoryMarshal.CreateSpan<T>(T, Int32) method to create a linear Span from a multidimensional array, then use Span<T>.CopyTo(Span<T>) method to copy the required data into or from the multidimensional array.

object[,] tableOfObjects = new object[3, 3]
{
    { 0, 1, 2 },
    { 3, 4, 5 },
    { 6, 7, 8 }
};

Span<object> tableSpan = MemoryMarshal.CreateSpan(ref tableOfObjects[0, 0], tableOfObjects.Length);
// tableSpan is linear here: [0, 1, 2, 3, 4, 5, 6, 7, 8]

object[] sourceRow = [9, 10, 11];
sourceRow.AsSpan().CopyTo(tableSpan.Slice(0, sourceRow.Length));
// tableOfObjects is now:
// {
//     { 9, 10, 11 },
//     { 3, 4, 5 },
//     { 6, 7, 8 }
// }

object[] destinationRow = new object[4];
tableSpan.Slice(1, destinationRow.Length).CopyTo(destinationRow);
// destinationRowOfObjects is now: [10, 11, 3, 4]

Alex · Accepted Answer · 2009-10-03 10:33:33Z

0

if I have gigabyte size arrays, I would do it in C++/CLI playing with pointers and doing just memcpy instead of having gazillion slow boundary-checked array indexing operations.

answered Oct 3, 2009 at 10:33

Alex

Comments

Gerry · Accepted Answer · 2021-03-24 21:23:39Z

0

I find it easiest to just do a loop.

public static double[,] arraycopy(double[] 
thearray, int n, int nrow, int ncol)
{

double[] sourcearray;
double[,] newarray;
int i = 0;
int j = 0;

sourcearray = new double[n];
sourcearray = thearray;
newarray = new double[nrow, ncol];
for(i=0; i<nrow; i++)
{
    for(j=0; j<ncol; j++)
        newarray[i,j] = sourcearray[nrow*i + j]; 
}

return newarray;

}

answered Mar 24, 2021 at 21:23

Gerry

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Comments

Justin Drury · Accepted Answer · 2009-07-08 16:56:10Z

-2

So, Something like:

    public static object[] GetRow()
    {
        object[,] test = new object[10,10];
        int a = 0;
        object[] row = new object[10];
        for(a = 0; a <= 10; a++)
        {
            row[a] = test[0, a];
        }
        return row;
    }

answered Jul 8, 2009 at 16:56

Justin Drury

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2 Comments

Guffa Over a year ago

That's the opposite; getting items from a two dimensional array into a one dimensional array. (Also, an array with the length 10 has index 0-9, not 0-10).

Justin Drury Over a year ago

whoops, my bad, I didn't actually run the code, I was just doing it from memory.

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