This code works fine:
var newArray = new Rectangle[newHeight, newWidth];
for (int x = 0; x < newWidth; x++)
for (int y = 0; y < newHeight; y++)
newArray[y, x] = (x >= width) || (y >= height) ? Rectangle.Empty : tiles[y, x];
But I am not having much luck replacing it with Array.Copy. Basically, if the resized array is larger it just adds blank rectangles to the edges. If it is smaller then it should just cut off the edges.
When doing this:
Array.Copy(tiles, newArray, newWidth * newHeight);
It messes up the array and all of its contents become disordered and do not retain their original index. Maybe I'm just having a brainfart or something?
Yes. However, it doesn't work the way you are thinking it works. Rather, it thinks of each mutlidimensional array as a single-dimensional array (which is actually what they are in memory, it's just a trick that lets us place some structure on top of them to think of them as multidimensional) and then copies the single-dimensional structures. So if you have
1 2 3
4 5 6
and want to copy it into
x x x x
x x x x
then it will think of the first array as
1 2 3 4 5 6
and the second as
x x x x x x x x
and the result will be
1 2 3 4 5 6 x x
which will appear to you as
1 2 3 4
5 6 x x
Got it?
I use this code:
public static void ResizeBidimArrayWithElements<T>(ref T[,] original, int rows, int cols)
{
T[,] newArray = new T[rows, cols];
int minX = Math.Min(original.GetLength(0), newArray.GetLength(0));
int minY = Math.Min(original.GetLength(1), newArray.GetLength(1));
for (int i = 0; i < minX; ++i)
Array.Copy(original, i * original.GetLength(1), newArray, i * newArray.GetLength(1), minY);
original = newArray;
}
calling like this for array of strings
ResizeBidimArrayWithElements<string>(ref arrayOrigin, vNumRows, vNumCols);
Simple use the "Clone()" function like the following:
This is your array list
object newArray = new object [row, column];
When you are creating another Array just use this code:
object[,] clonedArray = (object[,]) newArray.Clone();
Simple! Have fun!
I had a need to consume data from a buffer and copy off to a large holding array before the next interrupt hit. Copying in a loop wasn't an option; far too slow. I didn't need the multidimensional structure of the combined data until all of the copying was done, this meant I could Buffer.BlockCopy() to a single dimension array, then copy again onto a multidimensional array to obtain the required structure. Here's some code (run it in a console) that will demonstrate the technique as well as the performance.
static class Program
{
[STAThread]
static void Main()
{
Stopwatch watch = new Stopwatch();
const int width = 2;
const int depth = 10 * 1000000;
// Create a large array of data
Random r = new Random(100);
int[,] data = new int[width, depth];
for(int i = 0; i < width; i++)
{
for(int j = 0; j < depth; j++)
{
data[i, j] = r.Next();
}
}
// Block copy to a single dimension array
watch.Start();
int[] buffer = new int[width * depth];
Buffer.BlockCopy(data, 0, buffer, 0, data.Length * sizeof(int));
watch.Stop();
Console.WriteLine("BlockCopy to flat array took {0}", watch.ElapsedMilliseconds);
// Block copy to multidimensional array
int[,] data2 = new int[width, depth];
watch.Start();
Buffer.BlockCopy(buffer, 0, data2, 0,buffer.Length * sizeof(int));
watch.Stop();
Console.WriteLine("BlockCopy to 2 dimensional array took {0}", watch.ElapsedMilliseconds);
// Now try a loop based copy - eck!
data2 = new int[width, depth];
watch.Start();
for (int i = 0; i < width; i++)
{
for (int j = 0; j < depth; j++)
{
data2[i, j] = data[i, j];
}
}
watch.Stop();
Console.WriteLine("Loop-copy to 2 dimensional array took {0} ms", watch.ElapsedMilliseconds);
}
}
Output:
BlockCopy to flat array took 14 ms
BlockCopy to 2 dimensional array took 28 ms
Loop-copy to 2 dimensional array took 149 ms
Related
I know if I want to copy an array of the same type, I have at least 3 Options, I can use a double for loop, use Array.copy or Buffer.BulkCopy. The two copy methods are much faster. See for instance here: https://stackoverflow.com/a/33030421 .
Both copy methods allow you to only copy parts of the 2d array but Array.copy needs rank of source and destination to be equal while bulk.copy does not.
I get data from a com interface and doubles or int come through as object. Lets say I want to include a cast on the copy. I can do this:
Stopwatch watch = new Stopwatch();
const int width = 2;
const int depth = 10 * 1000000;
Random r = new Random(100);
object[,] objdata = new object[width, depth];
for (int i = 0; i < width; i++)
{
for (int j = 0; j < depth; j++)
{
objdata[i, j] = r.Next();
}
}
int[,] arr2dint = new int[width, depth];
watch.Reset();
watch.Start();
Array.Copy(objdata, 0, arr2dint, 0, objdata.GetLength(0) * objdata.GetLength(1));
watch.Stop();
Console.WriteLine("ArrayCopy to 2 dimensional array including cast took {0}", watch.ElapsedMilliseconds);
watch.Reset();
var bufferloopcast = new int[width, depth];
watch.Start();
for (int i = 0; i < width; i++)
{
for (int j = 0; j < depth; j++)
{
bufferloopcast[i, j] = (int)objdata[i, j];
}
}
watch.Stop();
Console.WriteLine("Loop-copy to 2 dimensional array including cast took {0} ms", watch.ElapsedMilliseconds);
Now the copy method is slower. Also it comes with the limitation that source and destination rank have to be equal so I cannot use it to copy only part of an array (say only the first row).
I cannot make the Buffer.BulkCopy to work, error must be primitive type. I tried this, in wain:
int[,] buff2dint = new int[width, depth];
watch.Reset();
watch.Start();
int sizeo = Marshal.SizeOf(objdata[0, 0]);
Buffer.BlockCopy(objdata, 0, buff2dint, 0, objdata.GetLength(0) * objdata.GetLength(1)* sizeo);
watch.Stop();
Console.WriteLine("BufferCopy to 2 dimensional array including cast took {0}", watch.ElapsedMilliseconds);
SO, why did array.copy become so slow? And what is the best method to copy an 2d array, or parts of it, if you need to include a cast?
What about using an array of arrays instead of a 2d-array?
int [][] buff2dint = new int[width][];
for(int i = 0; i < width; ++i)
{
buff2dint[i] = new int[depth];
Buffer.BlockCopy(srcArray, 0, buff2dint[i], depth);
}
I am trying to work towards a
512 x 512 (262144 elements)
I currently have a
List<double[,]> data;
Dimensions are:
4096 x [8 , 8] (262144 elements)
The 2d array I am working towards is square.
List<List<float>> newList = new List<List<float>(); //working towards
I have tried something along the lines of:
for (int i = 0; i < Math.Sqrt(data.Count); i++ ) {
List<float> row = new List<float>();
foreach (double[,] block in data) {
for (int j = 0; j < 8; j++) {
row.Add(block[i,j]); //i clearly out of range
}
}
newList.Add(row);
}
What I was trying to do there was to brute force my way and add up every row (which is 8 in length) and then add the large rows to the newList.
I believe you can do that in the following way
var newList = new List<List<float>>();
for (int i = 0; i < 512; i++)
{
var innerList = new List<float>();
for (int j = 0; j < 512; j++)
{
int x =(i/8)*64 + (j/8);
int y = i % 8;
int z = j % 8;
innerList.Add(data[x][y,z]);
}
newList.Add(innerList);
}
Basically you have 64x64 of your 8x8 blocks. So the (i,j) coordinate of the larger 512x512 structure translate in the following ways. First to determine the 8x8 block you have to figure out the row and column of the 64x64 structure of blocks by dividing the i and j by the size of the block (8) then you multiply the row (i/8) by the number of block in a row (64) and add the column (j/8). For the y and z it's simpler because you know that its just a matter of the remainder of i and j when divided by 8 (i%8) and (j%8).
I am wanting to create multiple arrays of ints(in C#). However they all must have a unique number in the index, which no other array has that number in that index. So let me try show you what I mean:
int[] ints_array = new int[30];
for (int i = 0; i < ints_array.Count(); i++)
ints_array[i] = i;
//create a int array with 30 elems with each value increment by 1
List<int[]> arrayList = new List<int[]>();
for(int i = 0; i < ints_array.Count(); i++)
arrayList.Add(ints_array[i]. //somehow sort the array here randomly so it will be unique
So I am trying to get the arrayList have 30 int[] arrays and each is sorted so no array has the same int in the same index as another.
Example:
arrayList[0] = {5,2,3,4,1,6,7,8,20,21... etc }
arrayList[1] = {1,0,5,2,9,10,29,15,29... etc }
arrayList[2] = {0,28,4,7,29,23,22,17... etc }
So would this possible to sort the array in this unique kind of way? If you need anymore information just ask and ill fill you in :)
Wouldn't it be easier to create the arrays iteratively using an offset pattern?
What I mean is that if you created the first array using 1-30 where 1 is at index 0, the next array could repeat this using 2-30 where 2 is at index 0 and then wrap back to 1 and start counting forward again as soon as you go past 30. It would be an easy and repeatable way to make sure no array shared the same value/index pair.
You can do it like that:
List<int[]> arrayList = new List<int[]>();
Random rnd = new Random();
for (int i = 0; i < ints_array.Length; i++)
{
ints_array = ints_array.OrderBy(x => rnd.Next()).ToArray();
var isDuplicate = arrayList.Any(x => x.SequenceEqual(ints_array));
if (isDuplicate)
{
while (arrayList.Any(x => x.SequenceEqual(ints_array)))
{
ints_array = ints_array.OrderBy(x => rnd.Next()).ToArray();
}
}
arrayList.Add(ints_array);
}
I think, this wouldn't be so efficient for bigger numbers than 30.But in this case it shouldn't be a problem, in my machine it takes 7 milliseconds.
Jesse's idea would be best unless you needed a pure random pattern. In that case I would recommend generating a random number, checking all your previous arrays, and then placing it in an array if it did not match any other arrays current index. Otherwise, generate a new random number until you find a fresh one. Put that into a loop until all your arrays are filled.
Use a matrix (2D-array). It is easier to handle than a list of arrays. Create a random number generator. Make sure to initialize it only once, otherwise random number generator may create bad random numbers, if created in too short time intervals, since the slow PC-clock might not have ticked in between. (The actual time is used as seed value).
private static Random random = new Random();
Create two helper arrays with shuffeled indexes for rows and columns:
const int N = 30;
int[] col = CreateUniqueShuffledValues(N);
int[] row = CreateUniqueShuffledValues(N);
Then create and initialize the matrix by using the shuffeled row and column indexes:
// Create matrix
int[,] matrix = new int[N, N];
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
matrix[row[i], col[j]] = (i + j) % N;
}
}
The code uses these two helper methods:
private static int[] CreateUniqueShuffledValues(int n)
{
// Create and initialize array with indexes.
int[] array = new int[n];
for (int i = 0; i < n; i++) {
array[i] = i;
}
// Shuffel array using one variant of Fisher–Yates shuffle
// http://en.wikipedia.org/wiki/Fisher-Yates_shuffle#The_modern_algorithm
for (int i = 0; i < n; i++) {
int j = random.Next(i, n);
Swap(array, i, j);
}
return array;
}
private static void Swap(int[] array, int i, int j)
{
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
int size = 10;
// generate table (no duplicates in rows, no duplicates in columns)
// 0 1 2
// 1 2 0
// 2 0 1
int[,] table = new int[size, size];
for (int y = 0; y < size; y++)
for (int x = 0; x < size; x++)
table[y, x] = (y + x) % size;
// shuffle rows
Random rnd = new Random();
for (int i = 0; i < size; i++)
{
int y1 = rnd.Next(0, size);
int y2 = rnd.Next(0, size);
for (int x = 0; x < size; x++)
{
int tmp = table[y1, x];
table[y1, x] = table[y2, x];
table[y2, x] = tmp;
}
}
// shuffle columns
for (int i = 0; i < size; i++)
{
int x1 = rnd.Next(0, size);
int x2 = rnd.Next(0, size);
for (int y = 0; y < size; y++)
{
int tmp = table[y, x1];
table[y, x1] = table[y, x2];
table[y, x2] = tmp;
}
}
// sample output
for (int y = 0; y < size; y++)
{
for (int x = 0; x < size; x++)
Console.Write("{0} ", table[y, x]);
Console.WriteLine();
}
Basically I'm working on an assignment and I need to move the values from a normal array to a 2D array. I have to take input to set the length of the aray. The 2d array will be a square array, so say 3 is input my array needs to be 3x3. I've made the 1D array size n*n, with n being what the user inputs. I'm getting an index out of rage exception but I've gone through the code and written out what I think the values of everything should be at each stage and can't find out what's causing it.
public static void createTwoD(int[,] twoDArray, int[] startArray, int arrayLength)
{
for (int x = 0; x < arrayLength; x++)
for (int i = 0; i < arrayLength; i++)
twoDArray[i, x] = startArray[i * arrayLength + x];
}
The line getting the exception is the last line in that method. I'm passing in a 2D array of size [n,n], a 1D array of size [n*n] and the just n. If you want to see any more of the code let me know.
The problem is in you lines:
for (int x = 0; x < arrayLength; x++)
for (int i = 0; i < arrayLength; i++)
twoDArray[i, x] = startArray[i * arrayLength + x];
arrayLength variable makes jump out of bounds on startArray. Note that both x and i are in range from 0 to arrayLength
If you know already dimensions of your 2d array, you can easily achieve this by (here I assume it 3x3):
var x = 0;
for (int i = 0; i < arrayLength; i++) {
if(i!= 0 && i % 3 == 0) ++x; // go to another row
twoDArray[i, x] = startArray[i];
}
I would start by adding the following to the start of your method. These document your assumptions about the dimensions of the arrays passed as arguments.
Debug.Assert(twoDArray.Rank == 2);
Debug.Assert(startArray.Rank == 1);
Debug.Assert(twoDArray.GetLength(0) == arrayLength);
Debug.Assert(twoDArray.GetLength(1) == arrayLength);
Debug.Assert(startArray.GetLength(0) == arrayLength * arrayLength);
maybe twoDArray issnt initilized correctly:
public static void createTwoD(int[,] twoDArray, int[] startArray, int arrayLength)
{
//twoDArray musst be initialized correctly, otherwise use:
twoDArray = new int[arrayLength][arrayLength];
for (int x = 0; x < arrayLength; x++)
for (int i = 0; i < arrayLength; i++)
twoDArray[i, x] = startArray[i * arrayLength + x];
}
I have read the question for Performance of 2-dimensional array vs 1-dimensional array
But in conclusion it says could be the same (depending the map own map function, C does this automatically)?...
I have a matrix wich has 1,000 columns and 440,000,000 rows where each element is a double in C#...
If I am doing some computations in memory, which one could be better to use in performance aspect? (note that I have the memory needed to hold such a monstruos quantity of information)...
If what you're asking is which is better, a 2D array of size 1000x44000 or a 1D array of size 44000000, well what's the difference as far as memory goes? You still have the same number of elements! In the case of performance and understandability, the 2D is probably better. Imagine having to manually find each column or row in a 1D array, when you know exactly where they are in a 2D array.
It depends on how many operations you are performing. In the below example, I'm setting the values of the array 2500 times. Size of the array is (1000 * 1000 * 3). The 1D array took 40 seconds and the 3D array took 1:39 mins.
var startTime = DateTime.Now;
Test1D(new byte[1000 * 1000 * 3]);
Console.WriteLine("Total Time taken 1d = " + (DateTime.Now - startTime));
startTime = DateTime.Now;
Test3D(new byte[1000,1000,3], 1000, 1000);
Console.WriteLine("Total Time taken 3D = " + (DateTime.Now - startTime));
public static void Test1D(byte[] array)
{
for (int c = 0; c < 2500; c++)
{
for (int i = 0; i < array.Length; i++)
{
array[i] = 10;
}
}
}
public static void Test3D(byte[,,] array, int w, int h)
{
for (int c = 0; c < 2500; c++)
{
for (int i = 0; i < h; i++)
{
for (int j = 0; j < w; j++)
{
array[i, j, 0] = 10;
array[i, j, 1] = 10;
array[i, j, 2] = 10;
}
}
}
}
The difference between double[1000,44000] and double[44000000] will not be significant.
You're probably better of with the [,] version (letting the compiler(s) figure out the addressing. But the pattern of your calculations is likely to have more impact (locality and cache use).
Also consider the array-of-array variant, double[1000][]. It is a known 'feature' of the Jitter that it cannot eliminate range-checking in the [,] arrays.