按子数组总大小将子数组拆分为Ruby

问题描述

我有一个子数组数组：

arr = [["a","b","c"],["a","b"],["c","v"],"f"],["e","a"],"n","m"],"c","g"]]

我想将每个子数组的元素放到另一个数组中，但是子数组的总和必须小于或等于6。所以我想得到类似这样的东西

[["a","a","v","f","e","m","g"]]

我现在的代码是

stop = 0
new_arr = []
indexo = ""
arr.each_with_index do |x,index|
   stop = stop + x.size
   if stop <= 6
      new_arr << x
      indexo = index
   end
end

我被困在这里，因为我的代码仅包含两个前元素。原始数组大约有1000个子数组，而我的代码并未将其拆分为这种形式。

解决方法

您可以使用reduce方法并继续将子数组推入新数组。请考虑以下内容：

new_arr = arr.reduce([]) do |acc,sub_array|
  last_element = acc[acc.length - 1]

  if last_element.nil? or (last_element + sub_array).length > 6
    acc << sub_array
  else
    acc[acc.length - 1] = last_element + sub_array
  end
  acc
end

# Tests
new_arr.flatten.size == arr.flatten.size # test total number of elements in both the arrays
new_arr.map(&:size) # the sizes of all sub arrays
new_arr.map(&:size).min # min size of all sub arrays
new_arr.map(&:size).max # max size of all sub arrays

让我知道代码是否不清楚

更新：

Reduce方法将通过遍历可枚举的每个元素来将任何可枚举的对象“还原”为单个值，就像each，map

考虑一个例子：

# Find the sum of array
arr = [1,2,3]

# Reduce will accept an initial value & a block with two arguments
#   initial_value: is used to set the value of the accumulator in the first loop

#   Block Arguments:
#   accumulator: accumulates data through the loop and finally returned by :reduce
#   value: each item of the above array in every loop(just like :each)

arr.reduce(0) do |acc,value|
  # initial value is 0; in the first loop acc's value will be set to 0
  # henceforth acc's value will be what is returned from the block in every loop

  acc += value
  acc # acc is begin returned; in the second loop the value of acc will be (0 + 1)
end

因此，在这种情况下，在每个循环中，我们将该项的值添加到累加器中，并返回累加器以在下一个循环中使用。一旦reduce迭代了数组中的所有项目，它将返回累加器。

Ruby还提供了语法糖以使其看起来更漂亮：

arr.reduce(:+) # return 6

很好article，以供进一步参考

因此，如果您以问题为例：

# Initial value is set to an empty array,what we're passing to reduce
new_arr = arr.reduce([]) do |acc,sub_array|
  # In the first loop acc's value will be set to []

  # we're finding the last element of acc (in first loop since the array is empty
  #    last element will be nil)
  last_element = acc[acc.length - 1]

  # If last_element is nil(in first loop) we push the first item of the array to acc
  # If last_element is found(pushed in the previous loops),we take it and sum
  #    it with the item from the current loop and see the size,if size is more
  #    than 6,we only push the item from current loop
  if last_element.nil? or (last_element + sub_array).length > 6
    acc << sub_array
  else
    # If last element is present & last_element + item from current loop's size
    #    is less than 6,we push the (last_element + item from current loop) into 
    #    the accumulator.
    acc[acc.length - 1] = last_element + sub_array
  end

  # Finally we return the accumulator,which will be used in the next loop
  # Or if has looped through the entire array,it will be used to return back
  #    from where it was called
  acc
end

,

arr = [["a","b","c"],["a","b"],["c","v"],"f"],["e","a"],"n","m"],"c","g"]]

arr.each_with_object([[]]) do |a,ar|
  if a.size + ar[-1].size > 6
    ar << a
  else
    ar[-1] += a
  end
end
  #=> [["a","a",#    ["c","v","f","e",#    ["a","m","g"]]

步骤如下。

enum = arr.each_with_object([[]])
  #=> #<Enumerator: [["a",...
  #     ["a","g"]]:each_with_object([[]])>

第一个值是由该枚举数生成的，并传递到块中，并且通过将Array Decomposition应用于传递到该块的两元素数组来为块值分配值。

a,ar = enum.next
   #=> [["a",[[]]] 
a  #=> ["a","c"] 
ar #=> [[]] 

请参见Enumerator#next。然后评估条件语句。

a.size + ar[-1].size > 6
  #=> 3 + 0 > 6 => false

所以我们执行：

ar[-1] += a
   #=> ["a","c"] 
ar #=> [["a","c"]]

下一个元素由enum生成，传递到块，并为块值分配值。

a,[["a","c"]]] 
a  #=> ["a","b"] 
ar #=> [["a","c"]]

条件语句被评估。

a.size + ar[-1].size > 6
  #=> 2 + 3 > 6 => false

所以我们再次执行：

ar[-1] += a
   #=> ["a","b"]]

enum然后将第三个元素传递到块。

a,"b"]]] 
a  #=> ["a","b"]] 

因为：

a.size + ar[-1].size > 6
  #=> 3 + 5 > 6 => false

这次我们执行

ar << a
  #=> [["a","c"]] 

其余步骤相似。