Ruby 注入索引和括号 [英] Ruby inject with index and brackets

问题描述

我尝试清理我的代码.第一个版本使用 each_with_index.在第二个版本中，我尝试使用 Enumerable.inject_with_index-construct 压缩代码，我发现了 这里.

I try to clean my Code. The first Version uses each_with_index. In the second version I tried to compact the code with the Enumerable.inject_with_index-construct, that I found here.

它现在可以工作了，但在我看来就像第一个代码一样晦涩难懂.更糟糕的是我不明白元素周围的括号，索引在

It works now, but seems to me as obscure as the first code. Add even worse I don't understand the brackets around element,index in

.. .inject(groups) do |group_container, (element,index)|

但它们是必要的

• 这些括号有什么用?
• 如何使代码清晰易读?

class Array

  # splits as good as possible to groups of same size
  # elements are sorted. I.e. low elements go to the first group,
  # and high elements to the last group
  # 
  # the default for number_of_groups is 4 
  # because the intended use case is
  # splitting statistic data in 4 quartiles
  # 
  # a = [1, 8, 7, 5, 4, 2, 3, 8]
  # a.sorted_in_groups(3) # => [[1, 2, 3], [4, 5, 7], [8, 8]]
  # 
  # b = [[7, 8, 9], [4, 5, 7], [2, 8]] 
  # b.sorted_in_groups(2) {|sub_ary| sub_ary.sum } # => [ [[2, 8], [4, 5, 7]], [[7, 8, 9]] ]
  def sorted_in_groups(number_of_groups = 4)
    groups = Array.new(number_of_groups) { Array.new }
    return groups if size == 0

    average_group_size = size.to_f / number_of_groups.to_f
    sorted = block_given? ? self.sort_by {|element| yield(element)} : self.sort

    sorted.each_with_index do |element, index|
      group_number = (index.to_f / average_group_size).floor 
      groups[group_number] << element
    end

    groups
  end
end

第二个版本 -- 带有注入"和索引

class Array
  def sorted_in_groups(number_of_groups = 4)
    groups = Array.new(number_of_groups) { Array.new }
    return groups if size == 0

    average_group_size = size.to_f / number_of_groups.to_f
    sorted = block_given? ? self.sort_by {|element| yield(element)} : self.sort

    sorted.each_with_index.inject(groups) do |group_container, (element,index)|
      group_number = (index.to_f / average_group_size).floor
      group_container[group_number] << element
      group_container
    end
  end
end

推荐答案

这些括号有什么用?

What is the use of these brackets?

这是 ruby​​ 的一个非常好的特性.我称之为解构数组赋值"，但它可能也有一个正式名称.

It's a very nice feature of ruby. I call it "destructuring array assignment", but it probably has an official name too.

这是它的工作原理.假设你有一个数组

Here's how it works. Let's say you have an array

arr = [1, 2, 3]

然后将这个数组分配给一个名称列表，如下所示:

Then you assign this array to a list of names, like this:

a, b, c = arr
a # => 1
b # => 2
c # => 3

你看，数组被解构"成它的单个元素.现在，到 each_with_index.如您所知，它就像一个常规的 each，但也返回一个索引.inject 不关心所有这些，它接受输入元素并将它们按原样传递给它的块.如果输入元素是一个数组(来自 each_with_index 的元素/索引对)，那么我们可以在块体中将其拆开

You see, the array was "destructured" into its individual elements. Now, to the each_with_index. As you know, it's like a regular each, but also returns an index. inject doesn't care about all this, it takes input elements and passes them to its block as is. If input element is an array (elem/index pair from each_with_index), then we can either take it apart in the block body

sorted.each_with_index.inject(groups) do |group_container, pair|
  element, index = pair

  # or
  # element = pair[0]
  # index = pair[1]

  # rest of your code
end

或者在块签名中解构该数组.有必要使用括号来提示 ruby​​ 这是一个需要拆分为多个的单个参数.

Or destructure that array right in the block signature. Parentheses there are necessary to give ruby a hint that this is a single parameter that needs to be split in several.

希望这会有所帮助.

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