如何在Haskell中创建数字列表 [英] How to create a list of list of numbers in Haskell

问题描述

我需要创建一个函数来制作一块行和列大小的板，然后用零填充它. mkBoard 2 3将使 [[0,0,0]，[0,0,0]]

I need to create a function that makes a board of size row and column and then populate that with zeros. mkBoard 2 3 would make [[0,0,0],[0,0,0]]

我真的不知道从哪里开始，因为我是Haskell编程的新手，我当时认为该函数应该是这样的:

I don't really know where to start as I am new to Haskell programming I was thinking that the function would be something like this:

mkBoard m n= [m | ???? take n (repeat 0)]

但是我不确定这是否是正确的方法.

But I am not sure if this would be the correct approach.

谢谢您的帮助.

推荐答案

正如@arrowd所述，take n (repeat x)有一个replicate函数.您可以使用replicate n 0创建木板的一行，然后创建诸如mkBoard m n = replicate m (replicate n 0)这样的行的木板.

As @arrowd already mentioned, there is a replicate function for take n (repeat x). You can create one row of your board with replicate n 0, and then create a board of such rows like mkBoard m n = replicate m (replicate n 0).

您还可以创建此函数的更通用版本，以使用任何值填充该字段:

Also you can create more generic version of this function to fill the field with any value:

genericMkBoard :: a -> Int -> Int -> [[a]]
genericMkBoard x m n = replicate m (replicate n x)

并使用部分应用程序定义:

mkBoard = genericMkBoard 0

UPD :您也可以使它与replicate更加一致(感谢@chepner):

UPD: Also you can make it like this to be more consistent with replicate (thanks to @chepner):

replicate2D m n x = replicate m (replicate n x)

mkBoard m n = replicate2D m n 0

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