如何初始化三维ruby数组

Question

I want to initialise a three dimensional ruby array. For a two-dimensional array, I can do

a = Array.new(4){ Array.new(5, 0) }

so I have tried

a = Array.new(4) { Array.new(5, Array.new(6, 0)) }

but if I do a[1][2][3] = 5 , it not only sets that element to 5 , it sets the corresponding element to 5 in other sub arrays ie

[[[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, 0, 0, 0, 0]],
 [[0, 0, 0, 5, 0, 0], [0, 0, 0, 5, 0, 0], [0, 0, 0, 5, 0, 0], [0, 0, 0, 5, 0, 0], [0, 0, 0, 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], [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, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0]]]

Answer 1

The issue is that if you pass the value as an argument, you will get an array where each value refers to that same object. You do exactly that with:

Array.new(5, Array.new(6, 0))

---

You can use Array#* , ie array multiplication instead:

[[[0] * 6] * 5] * 4

Answer 2

Just use the same syntax (with a block instead of an argument : Array.new(n){...} ) for all the dimensions.

a = Array.new(4) { Array.new(5) { Array.new(6, 0) } }

This way, your code will create 20 distincts Array.new(6, 0) sub-sub-arrays instead of replicating the same object 5 times.

require 'pp'
a = Array.new(4) { Array.new(5) { Array.new(6, 0) } }
a[1][2][3] = 5
pp a
# [[[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, 0, 0, 0, 0]],
#  [[0, 0, 0, 0, 0, 0],
#   [0, 0, 0, 0, 0, 0],
#   [0, 0, 0, 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],
#   [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, 0, 0, 0, 0],
#   [0, 0, 0, 0, 0, 0],
#   [0, 0, 0, 0, 0, 0],
#   [0, 0, 0, 0, 0, 0]]]

Answer 3

以下工作正常。

a=Array.new(4){ Array.new(5) { Array.new(6,0) }}

Answer 4

You can use recursion to initialize the elements of a multidimensional array of any dimension. ¹

Code

def init(n, *rest)
  rest.empty? ? Array.new(n, 0) : Array.new(n) { init(*rest) }
end

Examples

dims = [2, 3, 2]
a = init(*dims)
  #=> [[[0, 0], [0, 0], [0, 0]], [[0, 0], [0, 0], [0, 0]]]

a[0][0][0] = 1
a #=> [[[1, 0], [0, 0], [0, 0]], [[0, 0], [0, 0], [0, 0]]]

dims = [2, 3, 2, 4, 2, 3]
a = init(*dims)

a.flatten.size
  #=> 288 (= 2*3*2*4*2*3)
a[0][0][0][0][0][0] = 1
a.flatten.count(1)
  #=> 1

Explanation

The steps are as follows.

Suppose, as in the example,

dims = [2, 3, 2]

Then

n, *rest = dims
  #=> [2, 3, 2]
n #=> 2
rest
  #=> [3, 2]

As rest.empty? #=> false rest.empty? #=> false , the method returns

Array.new(2) { init(*[3, 2]) } # (1)
  #=> [[[0, 0], [0, 0], [0, 0]], [[0, 0], [0, 0], [0, 0]]]

To obtain this result, we execute the block

{ init(*[3, 2]) }

for each of the two elements of the array being constructed. This requires us to compute init([3, 2]) (same as { init(3, 2) } ), which is done as follows.

n, *rest = [3, 2]
  #=> [3, 2]
n #=> 3
rest
  #=> [2]

Again, as rest.empty? #=> false rest.empty? #=> false , we return

Array.new(3) { init(*[2]) } # (2)
  #=> [[0, 0], [0, 0], [0, 0]]

to expression (1) above. For each of the 3 elements of this array we execute the block

{ init(*[2]) }

This requires us to compute init([2]) , which is done as follows.

n, *rest = [2]
  #=> [2]
n #=> 2
rest 
  #=> []

This time, since rest.empty? #=> true rest.empty? #=> true , we compute and return

Array.new(2, 0)
  #=> [0, 0]

to expression (2) above.

^{1 Yes, there's no such thing as a "multidimensional array" in Ruby, but I expect readers to know what I mean. The alternative is something like "...of an array containing nested arrays of equal size with any number of levels of nesting", but even that is incomplete as it fails to exclude, for example, [[1, [2,3]], [4,5]] . It would be helpful if Ruby had a name for such objects.}