F#多维数组类型 [英] F# Multidimensional Array Types

问题描述

'a[,,]和'a[][][]有什么区别?它们都代表3维数组. 它使我写array3d.[x].[y].[z]而不是array3d.[x, y, z].

What's the difference between 'a[,,] and 'a[][][]? They both represent 3-d arrays. It makes me write array3d.[x].[y].[z] instead of array3d.[x, y, z].

为什么我不能执行以下操作?

Why I can't do the following?

> let array2d : int[,] = Array2D.zeroCreate 10 10;;
> let array1d = array2d.[0];;

error FS0001: This expression was expected to have type
    'a []    
but here has type
    int [,]

推荐答案

区别在于，'a[][]表示数组(长度可能不同)，而在'a[,]中表示矩形2D数组.第一种类型也称为锯齿状数组，第二种类型称为多维数组.区别与C#中的相同，因此您可能需要查看多维数组.在 F#Wiki 中也有一个出色的文档.

The difference is that 'a[][] represents an array of arrays (of possibly different lengths), while in 'a[,], represents a rectangular 2D array. The first type is also called jagged arrays and the second type is called multidimensional arrays. The difference is the same as in C#, so you may want to look at the C# documentation for jagged arrays and multidimensional arrays. There is also an excelent documentation in the F# WikiBook.

为了用图片演示这一点，类型为'a[][]的值可以看起来像这样:

To demonstrate this using a picture, a value of type 'a[][] can look like this:

0 1 2 3 4
5 6
7 8 9 0 1

a[,]类型的值将始终是矩形，并且可能看起来像这样:

While a value of type a[,] will always be a rectangle and may look for example like this:

0 1 2 3
4 5 6 7
8 9 0 1

---

要获取多维数组的单个线"，可以使用切片符号:

let row = array2d.[0,*];;

请参见 https://docs.microsoft.com/zh-cn/dotnet/fsharp/language-reference/arrays#array-slicing-and-multiDimension-arrays

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