ruby 中的数组数组，通过引用传递 [英] Array of Arrays in ruby, passed by reference

问题描述

我正在尝试在 Ruby 中创建一个 5x5 矩阵，其中填充了零.我使用的代码是:

I'm trying to create a 5x5 matrix in Ruby filled with zeroes. The code I used was:

ruby-1.9.2-p290 :014 > a = Array.new(5, Array.new(5, 0))
 => [[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]] 

然而，里面新创建的数组并不是单独的对象，而是对一个的引用.因此，当我尝试执行以下操作时:a[2][2] = 1 我得到:

However, the newly created arrays inside are not separate objects, but a reference to one. So when I try to do the following: a[2][2] = 1 I get:

=> [[0, 0, 1, 0, 0], [0, 0, 1, 0, 0], [0, 0, 1, 0, 0], [0, 0, 1, 0, 0], [0, 0, 1, 0, 0]] 

这显然不是我想要的.检查对象 ID 确认:

Which is obviously not what I want. Checking objects ids confirms it:

ruby-1.9.2-p290 :020 > a.collect {|z| z.__id__}.uniq
 => [70253724580020] 

我的问题是:这是错误还是功能?:) 我应该如何正确创建数组数组?

My questions is: is it a bug or feature? :) And how should I create array of arrays properly?

推荐答案

我正在尝试在 Ruby 中创建一个 5x5 矩阵，其中填充了零.我使用的代码是:

I'm trying to create a 5x5 matrix in Ruby filled with zeroes. The code I used was:

正如其他人所指出的，这就是数组应该如何工作.相反，您应该使用块初始值设定项:

As others have pointed out, this is how arrays are supposed to work. Instead, you should use the block initializer:

a = Array.new(5) { Array.new(5, 0) }

此外，如果您要制作矩阵，请考虑使用标准库中的 Matrix 类:

In addition, however, if you're making a matrix, consider using the Matrix class in the standard library:

require 'matrix'
 # => true 

m = Matrix.build(5, 5) { 0 }
 # => Matrix[[0, 0, 0, 0, 0],
 #           [0, 0, 0, 0, 0],
 #           [0, 0, 0, 0, 0],
 #           [0, 0, 0, 0, 0],
 #           [0, 0, 0, 0, 0]] 

m.determinant
 # => 0 

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