从阵列中创建一个哈希干净的方法 [英] Cleanest way to create a Hash from an Array

问题描述

我似乎经常遇到这样的。我需要阵列作为密钥使用的每个对象的属性从数组建立一个散列

可以说，我需要例如哈希使用由它们的ID键控的ActiveRecord objecs
常见的方式：

 元= [ActiveRecord对象的集合]
哈希= ary.inject（{}）{|哈希，OBJ |哈希[obj.id] = OBJ}
 

另一个方式：

 元= [ActiveRecord对象的集合]
哈希散列= [*（ary.map {| OBJ | [obj.id，OBJ]}）。压扁]
 

梦想之路：
我可以并可能制造出这个自己，但有使用Ruby或者Rails任何会这样？

 元= [ActiveRecord对象的集合]
哈希= ary.to_hash＆放大器;：ID
＃或者至少
哈希= ary.to_hash {| OBJ | obj.id}
 

解决方案

有已经在的ActiveSupport才会这样的方法。

  ['活动记录的'阵列'，'对象'] index_by。（安培;：ID）
 

和公正的记录，这里的实现：

 高清index_by
  注（{}）做| ACCUM，ELEM |
    ACCUM [产量（ELEM）] = ELEM
    ACCUM
  结束
结束
 

这本来是重构到（如果你的俏皮话是绝望）：

 高清index_by
  注（{}）{|哈希，ELEM | hash.merge！（收益率（ELEM）=＆GT; ELEM）}
结束
 

I seem to run into this very often. I need to build a Hash from an array using an attribute of each object in the array as the key.

Lets say I need a hash of example uses ActiveRecord objecs keyed by their ids Common way:

ary = [collection of ActiveRecord objects]
hash = ary.inject({}) {|hash, obj| hash[obj.id] = obj }

Another Way:

ary = [collection of ActiveRecord objects]
hash = Hash[*(ary.map {|obj| [obj.id, obj]}).flatten]

Dream Way: I could and might create this myself, but is there anything in Ruby or Rails that will this?

ary = [collection of ActiveRecord objects]
hash = ary.to_hash &:id
#or at least
hash = ary.to_hash {|obj| obj.id}

解决方案

There is already a method in ActiveSupport that does this.

['an array', 'of active record', 'objects'].index_by(&:id)

And just for the record, here's the implementation:

def index_by
  inject({}) do |accum, elem|
    accum[yield(elem)] = elem
    accum
  end
end

Which could have been refactored into (if you're desperate for one-liners):

def index_by
  inject({}) {|hash, elem| hash.merge!(yield(elem) => elem) }
end

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