如何在 Scala 中定义和初始化矩阵
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/25093483/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to define & init Matrix in Scala
提问by Alex L
I have a class which has two dimensional array as a private member - k rows and n columns (the size is not known when defining the Matrix).
我有一个类，它具有二维数组作为私有成员 - k 行和 n 列（定义矩阵时不知道大小）。
I want init the Matrix using a special method: initMatrix, which will set the number of rows and cols in the matrix, and init all the data to 0.
我想使用一种特殊的方法初始化矩阵：initMatrix，它将设置矩阵中的行数和列数，并将所有数据初始化为 0。
I saw a way to init a multi-dimensional array in the following way:
我看到了一种通过以下方式初始化多维数组的方法：
private var relationMatrix = Array.ofDim[Float](numOfRows,numOfCols)
but how can I define it without any size, and init it later?
但是我如何定义它没有任何大小，并在以后初始化它？
采纳答案by Radian
Did you consider using an Option?
你考虑过使用 Option 吗？
class MyClass() {
private var relationMatrix: Option[Array[Array[Float]]] = None
def initMatrix(numOfRows:Int, numOfCols:Int): Unit = {
relationMatrix = Some(/* Your initialization code here */)
}
}
The pros of this approach is that in any time you can know whether your matrix is initialized or not, by using relationMatrix.isDefined, or by doing pattern matching,
这种方法的优点是，您可以通过使用relationMatrix.isDefined或进行模式匹配，随时知道您的矩阵是否已初始化，
def matrixOperation: Float = relationMatrix match {
case Some(matrix) =>
// Matrix is initialized
case None =>
0 // Matrix is not initialized
}
or map on it, like this:
或在其上映射，如下所示：
def matrixOperation: Option[Float] = relationMatrix.map {
matrix: Array[Array[Float]] =>
// Operation logic here, executes only if the matrix is initialized
}
回答by elm
For declaring a mutable 2D array of floats without setting dimensions and values, consider
要在不设置维度和值的情况下声明可变的二维浮点数组，请考虑
var a: Array[Array[Float]] = _
a: Array[Array[Float]] = null
For initialising it consider the use of Array.tabulatelike this
为了初始化它考虑使用Array.tabulate这样的
def init (nRows: Int, nCols: Int) = Array.tabulate(nRows,nCols)( (x,y) => 0f )
Thus for instance,
因此，例如，
a = init(2,3)
delivers
提供
Array[Array[Float]] = Array(Array(0.0, 0.0, 0.0), Array(0.0, 0.0, 0.0))
Updatethe use of Option(already suggested by @Radian) proves type-safe and more robust at run-time, in contrast with nullinitialisation; hence, consider also Option(Array.tabulate).
Option与null初始化相比，更新使用（已由@Radian 建议）证明类型安全且在运行时更健壮；因此，还要考虑Option(Array.tabulate)。
回答by Ashalynd
You can make your initMatrix method part of the companion object.
您可以使您的 initMatrix 方法成为伴随对象的一部分。
class Matrix(numOfRows:Int, numOfCols:Int) {
private var relationMatrix = Array.ofDim[Float](numOfRows, numOfCols)
// your code there
}
object Matrix {
def initMatrix(numOfRows:Int, numOfCols:Int) = Matrix(numOfRows, numOfCols)
}
var myMatrix = Matrix.initMatrix(3,5)
回答by Display Name
var matrix: Array[Array[Float]] = null— this declares a variable of the same type as yours
var matrix: Array[Array[Float]] = null— 这声明了一个与你的类型相同的变量
