红宝石阵列，比较2个键和总结其他键/值

Question

在Ruby中，我有以下哈希值的数组：

[ 
    {:qty => 1, :unit => 'oz', :type => 'mass'}, 
    {:qty => 5, :unit => 'oz', :type => 'vol'}, 
    {:qty => 4, :unit => 'oz', :type => 'mass'}, 
    {:qty => 1, :unit => 'lbs', :type => 'mass'} 
] 

我需要能够做的是比较由:unit的元素和:type，然后在它们相同时总计:qty。将所得的阵列应该像如下：

[ 
    {:qty => 5, :unit => 'oz', :type => 'mass'}, 
    {:qty => 5, :unit => 'oz', :type => 'vol'}, 
    {:qty => 1, :unit => 'lbs', :type => 'mass'} 
] 

如果阵列具有多个散列，其中:qty是nil和:unit为空（""），那么这将只返回其中的一个。因此，要延长上面的例子，这样的：

[ 
    {:qty => 1, :unit => 'oz', :type => 'mass'}, 
    {:qty => nil, :unit => '', :type => 'Foo'}, 
    {:qty => 5, :unit => 'oz', :type => 'vol'}, 
    {:qty => 4, :unit => 'oz', :type => 'mass'}, 
    {:qty => 1, :unit => 'lbs', :type => 'mass'}, 
    {:qty => nil, :unit => '', :type => 'Foo'} 
] 

会变成这样：

[ 
    {:qty => 5, :unit => 'oz', :type => 'mass'}, 
    {:qty => nil, :unit => '', :type => 'Foo'}, 
    {:qty => 5, :unit => 'oz', :type => 'vol'}, 
    {:qty => 1, :unit => 'lbs', :type => 'mass'} 
] 

编辑：对不起，在第二个例子中犯了一个错误......它不应该有邻。

Answer 1

开始将每个值转换为单个散列值，或者使用nil（如果它们都是）：

properties.group_by do |property| 
    property.values_at :type, :unit 
end.map do |(type, unit), properties| 
    quantities = properties.map { |p| p[:qty] } 
    qty = quantities.all? ? quantities.reduce(:+) : nil 
    { type: type, unit: unit, qty: qty } 
end 

#=> [{:type=>"mass", :unit=>"oz", :qty=>5}, 
# {:type=>"Foo", :unit=>"", :qty=>nil}, 
# {:type=>"vol", :unit=>"oz", :qty=>5}, 
# {:type=>"mass", :unit=>"lbs", :qty=>1}] 

其中properties是您的第二个样本输入数据。

Answer 2

你会想enumberable.group_by

这应该让你使用group_by你想要的键，然后reduce的qty开始吧

items.group_by { |item| item.values_at(:unit, :type) } 

输出

{ 
    ["oz", "mass"]=> [ 
    {:qty=>1, :unit=>"oz", :type=>"mass"}, 
    {:qty=>4, :unit=>"oz", :type=>"mass"} 
    ], 
    ["oz", "vol"]=>[ 
    {:qty=>5, :unit=>"oz", :type=>"vol"} 
    ], 
    ["lbs", "mass"]=>[ 
    {:qty=>1, :unit=>"lbs", :type=>"mass"} 
    ] 
} 

Answer 3

ar = [{:qty => 1, :unit => 'oz', :type => 'mass'}, {:qty => nil, :unit => '', :type => 'Foo'}, 
     {:qty => 5, :unit => 'oz', :type => 'vol'}, 
     {:qty => 4, :unit => 'oz', :type => 'mass'}, {:qty => 1, :unit => 'lbs', :type => 'mass'}, 
     {:qty => nil, :unit => 'o', :type => 'Foo'}] 

result = ar.each_with_object(Hash.new(0)) do |e,hsh| 
    if hsh.has_key?({:unit => e[:unit], :type => e[:type]}) 
     hsh[{:unit => e[:unit], :type => e[:type]}] += e[:qty] 
    else 
     hsh[{:unit => e[:unit], :type => e[:type]}] = e[:qty] 
    end 
end 

result.map{|k,v| k[:qty] = v;k }.delete_if{|h| h[:qty].nil? and !h[:unit].empty? } 
# => [{:unit=>"oz", :type=>"mass", :qty=>5}, 
#  {:unit=>"", :type=>"Foo", :qty=>nil}, 
#  {:unit=>"oz", :type=>"vol", :qty=>5}, 
#  {:unit=>"lbs", :type=>"mass", :qty=>1}] 

---

以@Andrew马歇尔考虑

ar = [{:qty => 1, :unit => 'oz', :type => 'mass'}, {:qty => nil, :unit => '', :type => 'Foo'}, 
     {:qty => 5, :unit => 'oz', :type => 'vol'}, 
     {:qty => 4, :unit => 'oz', :type => 'mass'}, {:qty => 1, :unit => 'lbs', :type => 'mass'}, 
     {:qty => nil, :unit => 'o', :type => 'Foo'}] 

result = ar.each_with_object(Hash.new(0)) do |e,hsh| 
    if hsh.has_key?({:unit => e[:unit], :type => e[:type]}) 
     hsh[{:unit => e[:unit], :type => e[:type]}] += e[:qty] 
    else 
     hsh[{:unit => e[:unit], :type => e[:type]}] = e[:qty] 
    end 
end 

result.map{|k,v| k[:qty] = v;k }.delete_if{|h| h[:qty].nil? and h[:unit].empty? } 
# => [{:unit=>"oz", :type=>"mass", :qty=>5}, 
#  {:unit=>"oz", :type=>"vol", :qty=>5}, 
#  {:unit=>"lbs", :type=>"mass", :qty=>1}, 
#  {:unit=>"o", :type=>"Foo", :qty=>nil}]