仅在索引存在时编辑索引

Question

我需要创建一个代表图像的 0 和 1 的 2D 网格，并创建一个模糊方法，它将 1 旁边的任何 0（左、右、上或下）更改为 1，如下所示：

0000 => 0000
0000    0010
0010    0111
0000    0010

接下来我必须允许用户传入一个数字，该数字将允许模糊在每个方向上扩展多个空间。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 blur 来解释对角线。例如：

00000000 => 00010000
00000000    00111000
00010000    01111100
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(
  [0,0,0,0,0,0,0,0,0],
  [1,0,0,0,0,0,0,0,0],
  [0,0,0,0,0,0,0,0,0],
  [0,0,0,0,1,0,0,0,0],
  [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]
)
pic.blur(3)

我的函数有效，但前提是 1 不超出数组的边界。如果我把 1 放在角落里，看起来我的函数试图编辑一个不存在的索引的值，并且我收到以下消息：

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>'

我试图告诉它仅在索引存在时将 1 分配给索引。如有任何帮助，我将不胜感激。

Answer 1

看起来您要先检查两个级别，然后再检查一个级别。

例如，picture[1] 可能不存在...因此，如果您随后尝试检查 picture[i][j] 它会失败。

您可以尝试在索引之前检查每个级别是否存在...

if @picture[i] && @picture[i][j] && @picture[i][j] == 1
   if @blurred_image[i].present?
      @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]
   end
   @blurred_image[i-1][j] = 1 if @blurred_image[i-1] && @blurred_image[i-1][j] 
   @blurred_image[i+1][j] = 1 if @blurred_image[i+1] && @blurred_image[i+1][j] 

Answer 2

我的第一个想法是放弃这样的基于查找的解决方案：

adjacents = [[-1, 0], [0, -1], [0, 0], [1, 0], [0, 1]].freeze
@blurred_image = Array.new(@picture.length, 0) { Array.new(@picture[0].length, 0) }

@picture.each_index do |i|
  @picture[i].each_index do |j|
    if @picture[i][j] == 1
      adjacents.each { |x, y| (a = @blurred_image[i+x]) && a[j+y] &&= 1 }
    end
  end
end

请注意，&&= 运算符仅在左侧为真时才会执行赋值。所以它会失败，例如，如果你用 nil 值初始化你的内部数组。

Answer 3

感谢您的帮助。我昨晚看到了这个问题的另一个答案，但我认为海报出于某种原因删除了它？无论如何，我最终做了他们推荐的事情，即让我的 blurred_image 索引大于图像本身 - 基本上每个方向都有一个额外的行/列。然后当我向图像添加 1 时，我只是相应地调整了我的位置，以便图像仍然居中，然后我会在每次迭代结束时删除额外的行和列。我也可以尝试这些其他方法，但这种方法对我来说效果很好。

def blur(distance=1)
    #create new array of zeroes with 1 layer of extra 'padding', so any edges can push outwards without getting a nil error
    @blurred_image = Array.new(@picture.length+2, 0) {Array.new(@picture[0].length+2, 0)} 

    @picture.each_index do |i|
        @picture[i].each_index do |j|
            if @picture[i][j] == 1
                @blurred_image[i+1][j+1] = 1 
                @blurred_image[i+1][j]   = 1 
                @blurred_image[i+1][j+2] = 1 
                @blurred_image[i][j+1]   = 1 
                @blurred_image[i+2][j+1] = 1  
            end
        end     
    end

    #remove padding after checking and editing array to make it original size
    @blurred_image.pop
    @blurred_image.shift
    @blurred_image.each_index do |i|
        @blurred_image[i].pop
        @blurred_image[i].shift
    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