使用“each”方法将值分配给2D数组

I'm trying to transpose [[0, 1, 2], [3, 4, 5], [6, 7, 8]]. I get [[2, 5, 8], [2, 5, 8], [2, 5, 8]].

我试图转置[[0,1,2]，[3,4,5]，[6,7,8]]。我得到[[2,5,8]，[2,5,8]，[2,5,8]]。

I can see what is happening with the line p transposed_arr but do not understand why this is happening. At every iteration it changes every row instead of only one.

我可以看到行p transposed_arr发生了什么，但不明白为什么会发生这种情况。在每次迭代时，它都会更改每一行而不是一行。

def my_transpose(arr)
  # number of rows
  m = arr.count

  #number of columns
  n = arr[0].count

  transposed_arr = Array.new(n, Array.new(m))

  # loop through the rows
  arr.each_with_index do |row, index1|

      # loop through the colons of one row
      row.each_with_index do |num, index2|

          # swap indexes to transpose the initial array
          transposed_arr[index2][index1] = num
          p transposed_arr
      end
  end
  transposed_arr
end

1 个解决方案

#1

You need to make only one wee change and your method will work fine. Replace:

你需要只进行一次改变，你的方法才能正常工作。更换：

transposed_arr = Array.new(n, Array.new(m))

with:

有：

transposed_arr = Array.new(n) { Array.new(m) }

The former makes transposed_arr[i] the same object (an array of size m) for all i. The latter creates a separate array of size m for each i

前者使transposed_arr [i]成为所有i的相同对象（大小为m的数组）。后者为每个i创建一个单独的大小为m的数组

Case 1:

情况1：

transposed_arr = Array.new(2, Array.new(2))
transposed_arr[0].object_id
  #=> 70235487747860 
transposed_arr[1].object_id
  #=> 70235487747860

Case 2:

案例2：

transposed_arr = Array.new(2) { Array.new(2) }
transposed_arr[0].object_id
  #=> 70235478805680 
transposed_arr[1].object_id
  #=> 70235478805660

With that change your method returns:

通过该更改，您的方法返回：

[[0, 1, 2],
 [3, 4, 5],
 [6, 7, 8]]

#1