Develop Reference

"rotate" values in array clockwise

Firstly thank you for taking the time to look at my question.
I have a csv file of letters for which i need to get the last letter of the array and move it to the start while "pushing" the other letters across
E.G.
--Source--
a,b,c,d,[e]
--Rotated--
e,a,b,c,d
for (var i = 0; i < Array.Length - 1; i++)
{
temp = Array[Array.Length];
Array[Array.Length] = Array[Array.Length - 1];
Array[i + 1] = Array[i];
Array[i] = temp;
}
For this I am aware that not all characters would be effected but i cant think of a loop to get all values moved

Use Copy method:
int last = arr[arr.Length - 1];
Array.Copy(arr, 0, arr, 1, arr.Length - 1);
arr[0] = last;

You can shift the numbers to right by using the modulo % operator :
int[] arr = { 1, 2, 3, 4, 5 };
int[] newArr = new int[arr.Length];
for (int i = 0; i < arr.Length; i++)
{
newArr[(i + 1) % newArr.Length] = arr[i];
}
newArr = {5,1,2,3,4}
DEMO HERE
EDIT:
Or you could make a method that shifts the numbers in your initial array without the need for creating a new array. The method rightShiftArray takes two parameters, the initial array arr an the number of shifts (shift) you want to perform:
public void rightShiftArray(ref int[] arr, int shift)
{
for (int i = 0; i < shift; i++)
{
int temp;
for (int j = 0; j < arr.Length - 1; j++)
{
temp = arr[j];
arr[j] = arr[arr.Length - 1];
arr[arr.Length - 1] = temp;
}
}
}
For example:
int[] arr = { 1, 2, 3, 4, 5 };
rightShiftArray(ref arr, 2);
The code above shifts the numbers in the initial array arr twice to the right and gives you the following output:
arr = { 4, 5, 1, 2, 3};
DEMO HERE

if you doesn't want to allocate new array, you can use this code :
newValue = Array[Array.Length-1];
for (var i = 0; i < Array.Length; i++)
{
temp = Array[i];
Array[i] = newValue;
newValue = temp;
}

C#, Finding duplicates in arrays, Index was outside the bounds of the array

Can't figure out why the line winningNumbers[i] += count; comes up as outside the bounds of the array.
static int[] CheckWinningNumbers(int[][]lottoNumbers, int[]drawNumbers)
{
int[] winningNumbers = new int[8];
for (int i = 0; i < lottoNumbers.Length; i++)
{
int k = 0;
int count = 0;
for (int j = 0; j < lottoNumbers[i].Length; j++)
{
if (lottoNumbers[i][j] == drawNumbers[k])
{
count +=1;
}
k += 1;
winningNumbers[i] += count;
}
}
return winningNumbers;

Just replace
int[] winningNumbers = new int[8];
With
int[] winningNumbers = new int[lottoNumbers.Length];
As long as you are iterating lottoNumbers.Length the variable i will not exceed its boundaries.
Edit
I ran it with the following data and it works
int[][] lottoNumbers = { new[] { 1, 2 },
new[]{ 3, 4 },
new[]{ 5, 6 },
new[]{ 7, 8 } };
int[] drawNumbers = {1, 4, 5, 8};
I don't know what data you are testing it on but you are using jagged arrays intead of multidimensional. this will not guarantee that all your sub arrays have the same length which might be problematic. If all the arrays have the same length and performance is not critical here I'd suggest you use Multidimensional Arrays

How can I delete rows and columns from 2D array in C#?

How to delete a specific row and column from 2D array in C#?
int[,] array= {{1,2,3},{4,5,6},{7,8,9}};
lets say I want to delete row i and column i (skipping them) ... for nXn array not just 3x3 and store the remaining array in a new array...
so the output would be:
{5,6},{8,9}

There's no built-in way to do that, you can do it yourself:
static void Main()
{
int[,] array = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };
var trim = TrimArray(0, 2, array);
}
public static int[,] TrimArray(int rowToRemove, int columnToRemove, int[,] originalArray)
{
int[,] result = new int[originalArray.GetLength(0) - 1, originalArray.GetLength(1) - 1];
for (int i = 0, j = 0; i < originalArray.GetLength(0); i++)
{
if (i == rowToRemove)
continue;
for (int k = 0, u = 0; k < originalArray.GetLength(1); k++)
{
if (k == columnToRemove)
continue;
result[j, u] = originalArray[i, k];
u++;
}
j++;
}
return result;
}

No, arrays don't let you do that. You could make your own data structure for that, but it's not going to be exactly simple (unlike if you only wanted to be able to remove rows, for example).
For simple operations, it would be quite enough to build a class on top of an underlying array, and handle the re-indexing to map the virtual 2D array to the physical array underneath. But it's going to get a bit tricky as you combine removals and additions, and deform the array overall.

Very simple logic. Just play with the loop:
int[,] array = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };
int[,] arrayskip = new int[array.GetLength(0) - 1, array.GetLength(1) - 1];
for (int i = 1; i < array.GetLength(0); i++)
{
for (int j = 1; j < array.GetLength(1); j++)
{
arrayskip[i - 1, j - 1] = array[i, j];
}
}

I created this method, have a look
public static double[,] fillNewArr(double[,] originalArr, int row, int col)
{
double[,] tempArray = new double[originalArr.GetLength(0) - 1, originalArr.GetLength(1) - 1];
int newRow = 0;
int newCol = 0;
for (int i = 0; i < originalArr.GetLength(0); i++)
{
for (int j = 0; j < originalArr.GetLength(1); j++)
{
if(i != row && j != col)
{
tempArray[newRow, newCol] = originalArr[i, j];
newRow++;
newCol++;
}
}
}
return tempArray;
}
having some out of range, It's obvious why but I'm trying to get there...

Sum, Subtract and Multiply arrays

I've got the following arrays:
int[,] myArray1 = new int[2, 3] { { 1, 2, 3 }, { 4, 6, 8 } };
int[,] myArray2 = new int[2, 3] { { 6, 4, 3 }, { 8, 2, 8 } };
What I'd like to know how to do is:
Create a new array with the sum of myArray1 and myArray2
Create a new array with the subtraction of myArray1 and myArray2
Create a new array with the multiplication of myArray1 and myArray2
Result of sum would be:
int[,] myArray3 = new int[2, 3] { { 7, 6, 0 }, { -4, 4, 0 } };
Result of subtraction would be:
int[,] myArray3 = new int[2, 3] { { 5, 2, 6 }, { 12, 8, 16 } };
Result of multiplication would be:
int[,] myArray3 = new int[2, 3] { { 6, 8, 9 }, { 32, 12, 64 } };
Can this be done similar to printing out the arrays, with for loops? I tried looking for examples but found none that I could use for my specific problem.

int[,] a3 = new int[2,3];
for(int i = 0; i < myArray1.GetLength(0); i++)
{
for(int j = 0; j < myArray1.GetLength(1); j++)
{
a3[i,j] = myArray1[i,j] + myArray2[i,j];
a3[i,j] = myArray1[i,j] - myArray2[i,j];
a3[i,j] = myArray1[i,j] * myArray2[i,j];
}
}
need to store a3 before doing a new calculation obviously

For Sum:
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 3; j++)
{
myArray3[i, j] = myArray1[i, j] + myArray2[i, j];
}
}
For Subtraction:
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 3; j++)
{
myArray3[i, j] = myArray2[i, j] - myArray1[i, j];
}
}
For Multiplication:
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 3; j++)
{
myArray3[i, j] = A[i, j] * B[i, j];
}
}

Yes this would be done exactly like printing out the arrays with for loops
c# has foreach loops which would be even easier to use
Note: I get the idea this is for homework so I'm not going to give a 100% conclusive end all be all answer.
int[,] myArray1 = new int[2, 3] { { 1, 2, 3 }, { 4, 6, 8 } };
int[,] myArray2 = new int[2, 3] { { 6, 4, 3 }, { 8, 2, 8 } };
foreach (int[] a1 in myArray1)
{
foreach(int i in a1)
{
//operation here
//you get the idea
}
}

If you want to do array manipulation faster use the C# Parallel.For loop from System.Threading.Tasks:
For simple arithmetic parallelizing the outer loop is much faster than not on a modern PC processor. For more complex operations, or for small array sizes, the parallel version can be slower for various reasons.
Thus, use a stopwatch to time your matrix operations, and use the fastest solution. Parallelization makes doing array / image processing in C# much faster if implemented right.
Beware of overflowing your datatypes after arithmetic operations and also sharing variables between multiple threads (see System.Threading.Interlocked for help with that)...
Subtraction below. Similar for addition and multiplication:
Parallel.For(0, array.GetLength(1), y=>
{
for (int x = 0; x < array.GetLength(0); x++)
{
difference[x,y] = minuend[x,y] - subtrahend[x,y];
}
}
});

If you want to use a for loop, you can iterate through the rows/columns of the multi-d array as follows:
for (int i = 0; i < myArray1.GetLength(0); i++)
{
for (int j = 0; j < myArray1.GetLength(1); j++)
{
// Here, you can access the array data by index, using i and j.
// Ex, myArray1[i, j] will give you the value of 1 in the first iteration.
}
}
Note: When you pass a value into the Array's GetLength method, it represents the dimension of the array. See http://msdn.microsoft.com/en-us/library/system.array.getlength.aspx

How to reshape an Array in c#

I have a 3D array of bytes in c# which I have read from a bitmap:
byte[w, h, 3]
What is the easiest and more performance-friendly way of reshaping this array into 2D (linear) form?
byte[w*h, 3]
In other words I want to keep number of channels (features) but in a linear shape (rather than a square shape)
Let me try to illustrate input and desired output:
input:
|(r1,g1,b1) (r2,g2,b2) (r3,g3,b3)|
|(r4,g4,b4) (r5,g5,b5) (r6,g6,b6)|
|(r7,g7,b7) (r8,g8,b8) (r9,g9,b9)|
note that arr[0, 0, 0] = r1, arr[0, 0, 1] = g1, arr[0, 0, 2] = b1, etc..
and output:
|(r1,g1,b1) (r2,g2,b2) (r3,g3,b3) (r4,g4,b4) (r5,g5,b5) (r6,g6,b6) ...|

This seems to work fine, because the array is already in the right shape in memory:
var a = new byte[2, 2, 2] { { { 1, 2 }, { 3, 4 } }, { { 5, 6 }, { 7, 8 } } };
var b = new byte[2 * 2, 2];
//sizeof(byte) is obviously 1 here, but I put it there for documentation
Buffer.BlockCopy(a, 0, b, 0, a.Length * sizeof(byte));
For those interested: As for what to do if you really want to transpose a 2D array into 1D:
byte[,] a = {
{1, 2},
{3, 4},
{5, 6},
};
var b = new byte[a.GetLength(1) * a.GetLength(0)]; //Transpose
const int R_STRIDE1 = 8; //Tune this for your CPU
const int C_STRIDE1 = 8; //Tune this for your CPU
//You should hoist the calls to GetLength() out of the loop unlike what I do here
for (int r1 = 0; r1 < a.GetLength(0); r1 += R_STRIDE1)
for (int c1 = 0; c1 < a.GetLength(1); c1 += C_STRIDE1)
for (int r2 = 0; r2 < R_STRIDE1; r2++)
for (int c2 = 0; c2 < C_STRIDE1; c2++)
{
var r = r1 + r2;
var c = c1 + c2;
if (r < a.GetLength(0) && c < a.GetLength(1))
b[c * a.GetLength(0) + r] = a[r, c];
}
This should take advantage of caching in the CPU. I have only performed limited testing on this -- it could still be slow. Try tweaking it if it is.
You can (somewhat non-trivially) extend this to a 3D array.

Buffer.BlockCopy will do it. At least, it works in this simple test.
byte[, ,] src = new byte[10, 10, 3];
byte[,] dest = new byte[100, 3];
List<byte> srcList = new List<byte>();
Random rnd = new Random();
for (int i = 0; i < 10; ++i)
{
for (int j = 0; j < 10; ++j)
{
for (int k = 0; k < 3; ++k)
{
byte b = (byte)rnd.Next();
src[i, j, k] = b;
srcList.Add(b);
}
}
}
Buffer.BlockCopy(src, 0, dest, 0, 300);
List<byte> destList = new List<byte>();
for (int i = 0; i < 100; ++i)
{
for (int j = 0; j < 3; ++j)
{
destList.Add(dest[i, j]);
}
}
// See if they're in the same order
for (int i = 0; i < srcList.Count; ++i)
{
Console.WriteLine("{0,3:N0} - {1,3:N0}", srcList[i], destList[i]);
if (srcList[i] != destList[i])
{
Console.WriteLine("ERROR!");
}
}
That said, I wouldn't use Buffer.BlockCopy in this way unless I was absolutely sure that there weren't odd cases with padding issues, etc. And although Buffer.BlockCopy is certainly faster than the equivalent explicit loop, it shouldn't materially affect the runtime of your program. Unless you're doing this conversion inside a piece of code that's called very, very often ... in which case you have bigger problems.
I would suggest writing the explicit loop.

As an alternative you might want to use System.Numerics.Tensors:
It makes reshaping very easy:
using System.Numerics.Tensors;
..
var src = new byte[3, w, h]
var dst = ArrayTensorExtensions
.ToTensor(src)
.Reshape(new[] { 3, w * h });