ruby中嵌套的一些数组元素,每个块都变成nil

dy1byipe 于 2023-04-20 发布在 Ruby

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我希望每个数组元素都与其他数组元素交互。然而，我的代码中的某些元素具有意外的值nil。
如何避免这种不受欢迎的行为？
下面是合并元素的代码：（它只打印对）

def remove_sum_of_zero(arr)
  arr.each do |n|
    arr.each do |x|
      unless arr.index(n) == arr.index(x)
        puts "#{arr[n]} is being checked with #{arr[x]}"
      end
    end
  end
end

numArr = [3, 4, -7, 5, -6, 6]
remove_sum_of_zero(numArr)

输出：

5 is being checked with -6
5 is being checked with
5 is being checked with 6
5 is being checked with 3
5 is being checked with
-6 is being checked with 5
-6 is being checked with
-6 is being checked with 6
-6 is being checked with 3
-6 is being checked with
is being checked with 5
is being checked with -6
is being checked with 6
is being checked with 3
is being checked with
6 is being checked with 5
6 is being checked with -6
6 is being checked with
6 is being checked with 3
6 is being checked with
3 is being checked with 5
3 is being checked with -6
3 is being checked with
3 is being checked with 6
3 is being checked with
is being checked with 5
is being checked with -6
is being checked with
is being checked with 6
is being checked with 3

我尝试使用不同的数组，每次不同的值都变成nil。

ruby

来源：https://stackoverflow.com/questions/76054120/ruby-some-array-elements-in-nested-each-block-become-nil

1条答案

按热度按时间

x8goxv8g1#

each产生的是元素，而不是它们的索引，即n变成了3、4、-7、5等。
如果你好奇Ruby中数组索引是如何工作的，负索引从数组的末尾开始计数，-1是最后一个元素：

numArr = [ 3,  4, -7,  5, -6,  6]
#          0   1   2   3   4   5   6 ... ← positive indices (and 0)
# ... -7  -6  -5  -4  -3  -2  -1         ← negative indices

如果你需要元素和它的索引，有each_with_index，它同时产生两个值：

def remove_sum_of_zero(arr)
  arr.each_with_index do |a, i|
    arr.each_with_index do |b, j|
      next if i == j

      puts "#{a} is being checked with #{b}"
    end
  end
end

或者你可以使用permutation，它可以产生所有对：（同上）

def remove_sum_of_zero(arr)
  arr.permutation(2) do |a, b|
    puts "#{a} is being checked with #{b}"
  end
end

或者，如果将a与b进行比较等同于将b与a进行比较（即，如果元素的顺序无关），则可能需要combination，它省略了那些“重复”：

def remove_sum_of_zero(arr)
  arr.combination(2) do |a, b|
    puts "#{a} is being checked with #{b}"
  end
end

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ruby中嵌套的一些数组元素,每个块都变成nil

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