Iterate array and leave one out in each step

Question

How do I iterate the elements of an array in Ruby and in each step I can do something with the array containing all elements, except the one that is iterated in the moment?

For instance for [4,2,8] I iterate the elements and then I can do something with

• [2,8]
• [4,8]
• [4,2]

Answer 1

It's not really directly possible (unless you do not need the missing element). But you can program it yourself:

Option 1 - just do it :

a = [11,22,33,44,55]

a.each_with_index { |e,i|
  p e
  p a.take(i) + a[i+1..-1]
}

Option 2 - integrate with Array :

class Array
  def each_excluded(&block)
    self.each_with_index { |e, i|
      yield(e, self.take(i) + self[i+1..-1])
    }
  end
end

a.each_excluded { |e, rest|
  p e
  p rest
}

Output from either one:

11
[22, 33, 44, 55]
22
[11, 33, 44, 55]
33
[11, 22, 44, 55]
44
[11, 22, 33, 55]
55
[11, 22, 33, 44]

Answer 2

您可以使用slice方法并使用包含索引的项目创建一个新数组。

Answer 3

[4, 2, 8].tap{|a| a.length.times{|i| 
  do_something_you_want_with(a[0...i]+a[i+1..-1])
}}

or

class Array
  def each_but_one &pr
    length.times{|i| pr.call(self[0...i]+self[i+1..-1])}
  end
end

[4, 2, 8].each_but_one{|a| do_something_you_want_with(a)}

Answer 4

It really looks like you want Array#combination :

[4,2,8].combination(2).each do |ary|
  p ary
end

Which outputs:

[4, 2]
[4, 8]
[2, 8]

Each sub-array created is yielded to the block, in this case to ary , so you can do what you want with the values.