copy values from Object[,] Array to Object[][] Array

Question

I have two Arrays:

an object[,] Array
an object[][] Array.

I want to copy the values from the object[,] array to the object[][] array.

I have tried something like that

object[,] array1 = new object[arraySize, 4]; //Here are some values inside
object[][] array2 = new object[arraySize][];


for (int i = 0; i < arraySize; i++)
{
    array2[i][0] = array1[i, 0];
    array2[i][1] = array1[i, 1];
    array2[i][2] = array1[i, 2];
    array2[i][3] = array1[i, 3];
    
}

But I got a NullReferenceException:

Object reference not set to an instance of an object.

You got the direction of your assignments wrong.

Mo B.
– Mo B.

2020-09-24 08:37:44 +00:00
Commented Sep 24, 2020 at 8:37 — Mo B.
– Mo B., Commented Sep 24, 2020 at 8:37
And why are you using arrayCounter2 and not just i?

Mo B.
– Mo B.

2020-09-24 08:38:49 +00:00
Commented Sep 24, 2020 at 8:38 — Mo B.
– Mo B., Commented Sep 24, 2020 at 8:38
i have edited, thank you

tzumd
– tzumd

2020-09-24 08:42:57 +00:00
Commented Sep 24, 2020 at 8:42 — tzumd
– tzumd, Commented Sep 24, 2020 at 8:42

Pedro Perez · Accepted Answer · 2020-09-24 09:29:29Z

1

array2[i][0] = array1[i, 0];

Here you have a null reference exception because array2[i] is null. You need to initialize each element of array2 before you can use.

A jagged array is an array of arrays, and therefore its elements are reference types and are initialized to null.

microsoft documentation

// In your code, `arraySize` correspond to the numbers of rows in a multidimensional array. 
// In this example, rows = 2, columns = 4.
object[,] array1 = new object[2, 4] { { 1, 2, 3, 4 }, { 5, 6, 7, 8 } };
object[][] array2 = new object[2][] { new object[4], new object[4] };

for (int x = 0; x < 2; x++)
{
    for (int y = 0; y < 4; y++)
    {
        array2[x][y] = array1[x, y];
    }
}

// print array2
for (int i = 0; i < array2.Length; i++)
{
    Console.WriteLine(string.Join(",", array2[i]));
}

Console.ReadLine();

edited Sep 24, 2020 at 9:29

answered Sep 24, 2020 at 8:48

Pedro Perez

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Comments

Mo B. · Accepted Answer · 2020-09-24 11:25:22Z

1

Try this:

for (int i = 0; i < array1.GetLength(0); i++)
{
    array2[i] = new object[array1.GetLength(1)]; // array2[i] is null initially
    for(int j = 0; j < array1.GetLength(1); j++) {           
        array2[i][j] = array1[i, j];
    }
}

Try it out here: https://dotnetfiddle.net/f1XUXI

edited Sep 24, 2020 at 11:25

answered Sep 24, 2020 at 8:44

Mo B.

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2 Comments

tzumd Over a year ago

thaks, but got the same exception: NullReferenceException: Object reference not set to an instance of an object.

Mo B. Over a year ago

I added a fiddle so you can see it in action.

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