将 2 元素数组的数组转换为哈希，其中重复的键附加附加值 [英] Convert array of 2-element arrays into a hash, where duplicate keys append additional values

问题描述

给定一个数组:

array = [[:a,:b],[:a,:c],[:c,:b]]

返回以下哈希:

hash = { :a => [:b,:c] , :c => [:b] }

hash = Hash[array] 覆盖之前的关联，产生:

hash = Hash[array] overwrites previous associations, producing:

hash = { :a => :c , :c => :b }

推荐答案

使用函数式婴儿步骤:

irb:01.0> array = [[:a,:b],[:a,:c],[:c,:b]]
#=> [[:a, :b], [:a, :c], [:c, :b]]

irb:02.0> array.group_by(&:first)
#=> {:a=>[[:a, :b], [:a, :c]], :c=>[[:c, :b]]}

irb:03.0> array.group_by(&:first).map{ |k,a| [k,a.map(&:last)] }
#=> [[:a, [:b, :c]], [:c, [:b]]]

irb:04.0> Hash[ array.group_by(&:first).map{ |k,a| [k,a.map(&:last)] } ]
#=> {:a=>[:b, :c], :c=>[:b]}

使用命令式编程:

irb:10.0> h = Hash.new{ |h,k| h[k]=[] }
#=> {}

irb:11.0> array.each{ |k,v| h[k] << v }
#=> [[:a, :b], [:a, :c], [:c, :b]]

irb:12.0> h
#=> {:a=>[:b, :c], :c=>[:b]}

作为一个命令式的单行:

As an imperative one-liner:

irb:13.0> h = Hash.new{ |h,k| h[k]=[] }.tap{ |h| array.each{ |k,v| h[k] << v } }
#=> {:a=>[:b, :c], :c=>[:b]}

或者使用大家最喜欢的inject:

Or using everyone's favorite inject:

irb:14.0> array.inject(Hash.new{ |h,k| h[k]=[] }){ |h,(k,v)| h[k] << v; h }
#=> {:a=>[:b, :c], :c=>[:b]}

如果您真的希望单个值不会作为数组发生碰撞，您可以将它们取消排列作为后处理步骤，或者使用不同的哈希累积策略，仅在碰撞时创建数组.或者，把你的头围绕在这个:

If you really want to have single values not collided as an array, you can either un-array them as a post-processing step, or use a different hash accumulation strategy that only creates an array upon collision. Alternatively, wrap your head around this:

irb:17.0> hashes = array.map{ |pair| Hash[*pair] } # merge many mini hashes
#=> [{:a=>:b}, {:a=>:c}, {:c=>:b}]

irb:18.0> hashes.inject{ |h1,h2| h1.merge(h2){ |*a| a[1,2] } }
#=> {:a=>[:b, :c], :c=>:b}

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