数组 – 仅在索引存在时编辑索引

0000 => 0000
0000    0010
0010    0111
0000    0010

接下来,我必须允许用户传入一个允许模糊在每个方向上扩展多个空格的数字.如果我调用image.blur(2),它会在每个方向上扩展2个空格,但每个第一步都必须再次调用模糊以考虑对角线.例如：

00000000 => 00010000
00000000    00111000
00010000    02222200
00000000    00111000
00000000    00010000

这是我的代码.

class Image
  attr_accessor :picture
  def initialize(*rows)
    @picture = *rows
  end
  def output_image
    @picture.each_index do |i|
      puts @picture[i].join
    end
  end
  def blur(distance=1)
    @blurred_image = Array.new(@picture.length,0) {Array.new(@picture[0].length,0)} #create new array of zeroes the size of @picture
    @picture.each_index do |i|
      @picture[i].each_index do |j|
        if @picture[i][j] == 1
          @blurred_image[i][j]   = 1 if @blurred_image[i][j] 
          @blurred_image[i][j-1] = 1 if @blurred_image[i][j-1] 
          @blurred_image[i][j+1] = 1 if @blurred_image[i][j+1] 
          @blurred_image[i-1][j] = 1 if @blurred_image[i-1][j] 
          @blurred_image[i+1][j] = 1 if @blurred_image[i+1][j] 
        end
      end       
    end
    if distance > 1
      @picture = @blurred_image #save progress of image blur in @picture so we can continue in recursive call 
      blur(distance-1) #iterate as long as distance > 1
      elsif distance == 1 #necessary so blurred image isn't printed 'distance' times
      @blurred_image.each_index do |i|
        puts @blurred_image[i].join
      end
    end
  end
end

pic = Image.new(
  [0,0],[1,[0,1,0]
)
pic.blur(3)

我的函数可以正常工作,但前提是1不超出数组的范围.如果我在角落放一个1,看起来我的函数试图编辑一个不存在的索引的值,我得到以下消息：

image_blur.rb:28:in `block (2 levels) in blur': undefined method `[]' for nil:NilClass (NoMethodError)
from image_blur.rb:22:in `each_index'
from image_blur.rb:22:in `block in blur'
from image_blur.rb:21:in `each_index'
from image_blur.rb:21:in `blur'
from image_blur.rb:35:in `blur'
from image_blur.rb:35:in `blur'
from image_blur.rb:47:in `<main>'

我试图告诉它只在索引存在的情况下将1分配给索引.我很感激任何帮助.