从2维数组中提取数据并创建一个包含数组值的散列 [英] extracting from 2 dimensional array and creating a hash with array values

问题描述

我有一个2维数组

  v = [[ab，12]，[ab ，31]，[gh，54]] 
  

v的子数组将具有重复元素，例如ab。我想创建一个散列，将键作为子数组的第一个元素，并将值作为来自 v 的相应第二个元素的数组。 b

请指教。

另外，我想这个，h = {ab=> [12，31]， gh=> [54]}然后我想返回h.values，这样返回数组[[12，31]，[54]]

解决方案

  v.inject（Hash.new {| h，k | h [k] = []}） {| h，（k，v）| h [k]<< v; h} 
  

功能：

• 注入 a>（也称为 reduce ）是折叠。 Wikipedia定义了这样的折叠：一系列高阶函数，它们分析递归数据结构，并通过使用给定的组合操作重组处理其组成部分的结果，建立返回值 。




• Hash.new 带有两个参数，散列本身和密钥。如果您的默认参数是可变对象，则必须以此方式设置默认值，否则所有键都将指向同一个数组实例。

c $ c>注入的块，我们得到两个参数，散列值和迭代的当前值。由于这是一个二元数组，因此使用（k，v）将后者解构为两个变量。



• 最后，我们将每个值添加到数组中作为其键，并返回整个哈希值以用于下一次迭代。

I have a 2 dimensional array

v = [ ["ab","12"], ["ab","31"], ["gh","54"] ]

The first element of the subarray of v will have repeating elements, such as "ab". I want to create a hash that puts the key as the first element of the subarray, and values as an array of corresponding second elements from v.

please advice.

Further, I want this, h={"ab"=>["12","31"],"gh"=>["54"]} and then I want to return h.values, such that the array [["12","31"],["54"]] is returned

解决方案

v.inject(Hash.new{|h,k|h[k]=[]}) { |h, (k, v)| h[k] << v ; h}

What it does:

• inject (also called reduce) is a fold. Wikipedia defines folds like this: "a family of higher-order functions that analyze a recursive data structure and recombine through use of a given combining operation the results of recursively processing its constituent parts, building up a return value".

• The block form of Hash.new takes two arguments, the hash itself and the key. If your default argument is a mutable object, you have to set the default this way, otherwise all keys will point to the same array instance.

• In inject's block, we get two arguments, the hash and the current value of the iteration. Since this is a two element array, (k, v) is used to destructure the latter into two variables.

• Finally we add each value to the array for its key and return the entire hash for the next iteration.

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