如何从二维数组中获取一维列数组和一维行数组？(C#.NET)
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How to get 1D column array and 1D row array from 2D array? (C# .NET)
提问by Jose Kiwi
i have double[,] Array;. Is it possible to get something like double[] ColumnArray0 = Array[0,].toArray()and double[] RowArray1 = Array[,1].toArray()without making a copy of every elemet(using for)?
我有double[,] Array;。是否有可能得到的东西像double[] ColumnArray0 = Array[0,].toArray()和double[] RowArray1 = Array[,1].toArray()无（使用）使每一个elemet的副本？
Thanks.
谢谢。
采纳答案by thalm
Arrays are a memory area where all entries are stored in a consecutive way. Depending on the data layout in memory this is only possible for either rows or columns.
数组是一个内存区域，所有条目都以连续方式存储在其中。根据内存中的数据布局，这仅适用于行或列。
Instead of the 2d array double[,]type it is in your case better to use an array of arrays double[][]
double[,]在您的情况下，最好使用数组数组而不是 2d 数组类型double[][]
double[][] Array2d = new double[10][];
Array2d[0] = new double[10];
Array2d[1] = new double[10];
...
and then:
double[] RowArray0 = Array2d[0];
Depending on how you put the data in your array, you can also treat the Array2das a column array. But to have both at the same time is not possible.
根据您将数据放入数组的方式，您还可以将其Array2d视为列数组。但同时拥有两者是不可能的。
Also have a look here: Multidimensional Array [][] vs [,]
也看看这里： 多维数组 [][] vs [,]
回答by Timitry
Although being very late, I want to provide an alternative answer to the question.
虽然很晚了，但我想为这个问题提供一个替代答案。
The first important part of the question was to be able to access complete rows OR columns of the matrix. One possibility of doing this is by using extension methods:
问题的第一个重要部分是能够访问矩阵的完整行或列。这样做的一种可能性是使用扩展方法：
public static class MatrixExtensions
{
/// <summary>
/// Returns the row with number 'row' of this matrix as a 1D-Array.
/// </summary>
public static T[] GetRow<T>(this T[,] matrix, int row)
{
var rowLength = matrix.GetLength(1);
var rowVector = new T[rowLength];
for (var i = 0; i < rowLength; i++)
rowVector[i] = matrix[row, i];
return rowVector;
}
/// <summary>
/// Sets the row with number 'row' of this 2D-matrix to the parameter 'rowVector'.
/// </summary>
public static void SetRow<T>(this T[,] matrix, int row, T[] rowVector)
{
var rowLength = matrix.GetLength(1);
for (var i = 0; i < rowLength; i++)
matrix[row, i] = rowVector[i];
}
/// <summary>
/// Returns the column with number 'col' of this matrix as a 1D-Array.
/// </summary>
public static T[] GetCol<T>(this T[,] matrix, int col)
{
var colLength = matrix.GetLength(0);
var colVector = new T[colLength];
for (var i = 0; i < colLength; i++)
colVector[i] = matrix[i, col];
return colVector;
}
/// <summary>
/// Sets the column with number 'col' of this 2D-matrix to the parameter 'colVector'.
/// </summary>
public static void SetCol<T>(this T[,] matrix, int col, T[] colVector)
{
var colLength = matrix.GetLength(0);
for (var i = 0; i < colLength; i++)
matrix[i, col] = colVector[i];
}
}
Usage example:
用法示例：
double[,] myMatrix = ... // Initialize with desired size and values.
double[] myRowVector = myMatrix.GetRow(2); // Gets the third row.
double[] myColVector = myMatrix.GetCol(1); // Gets the second column.
myMatrix.SetCol(2, myColVector); // Sets the third column to the second column.
First thing to note is that you can use these generic methods with any kind of [,]-matrices and corresponding []-vectors. Imagine replacing the Ts with doubles, and you would get the specific version for 'double' (as was asked by the OP).
首先要注意的是，您可以将这些通用方法与任何类型的 [,] 矩阵和相应的 [] 向量一起使用。想象一下用Ts替换doubles，您将获得“double”的特定版本（正如 OP 所要求的那样）。
Second thing is, that getting and setting the rows uses Array.Copy, while getting and setting the columns uses a loop. This is due to the Row-Major orderof C#, which allows the first, but not the second. Of course both can be implemented with a loop, as seen commented out.
第二件事是，获取和设置行使用Array.Copy，而获取和设置列使用循环。这是由于C#的Row-Major 顺序，它允许第一个，但不允许第二个。当然，两者都可以用循环实现，如注释所示。
Make sure to pass correct dimensions for the set-Methods, or the program will crash (error and dimension checking can be added easily). The whole logic could as well be implemented for jagged arrays like double[][], however, the OP specificially asked for multidimensional ones.
确保为 set-Method 传递正确的维度，否则程序将崩溃（可以轻松添加错误和维度检查）。整个逻辑也可以为锯齿状数组实现，例如double[][]，但是，OP 特别要求多维数组。
As for the second part of the question: If your matrix consists of double, and since double is a value type, the values will always be copied. So your desired behaviour of not copying the values would not be possible. However, if using objects as T, only the reference pointing to the object will be copied, and not the object itself (so beware of mutating the 'copied' object).
至于问题的第二部分：如果您的矩阵由 double 组成，并且由于 double 是值类型，则将始终复制这些值。所以你想要的不复制值的行为是不可能的。但是，如果使用对象 as T，则只会复制指向该对象的引用，而不是对象本身（因此请注意“复制”对象的变异）。
Lastly, if you really don't want to copy the double-values, I'd suggest passing your whole matrix (only the reference is passed), and then directly looping through the desired columns and/or rows.
最后，如果您真的不想复制双值，我建议传递整个矩阵（仅传递引用），然后直接循环遍历所需的列和/或行。
