Grouping via an element in hash [closed]

问题

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Closed 6 years ago.

Suppose I have this array

x=[{:shipping_id=>2, :fsn=>"ab", :price=>300, :quantity=>1},
   {:shipping_id=>3, :fsn=>"abc",:price=>500, :quantity=>2},
   {:shipping_id=>2, :fsn=>"abcd",:price=>300,:quantity=>3},
   {:shipping_id=>4, :fsn=>"abx", :price=>600,:quantity=>1},
   {:shipping_id=>3, :fsn=>"abb", :price=>400,:quantity=>1}] 

I want to group it by unique shipping id, but in this case let us just group by shipping_id=2

So I do x.select! {|y| y[:shipping_id]==2} which gives me

[{:shipping_id=>2, :fsn=>"ab",:price=>300,:quantity=>1}, {:shipping_id=>2, :fsn=>"abcd",:price=>300,:quantity=>3}]

But the problem is I want my result in this form

x={:shipping_id=>[2,2],:fsn=>["ab","abcd"],:price=>[300,300],:quantity=>[1,3]}

What should I do? I can do this in a few lines, but is there any optimized way for it?

UPDATE -: Final working solution (My solution)-

Controller

 new_params={}
 order_hash.each do |row|
        new_params=row.convert_to_params(new_params)
 end
 params.merge!(new_params)

Model

 def convert_to_params(new_params)
    item=self.instance_values.symbolize_keys
    item.each do |k, v|
      new_params[k].nil? ? new_params[k]=[v] : new_params[k].push(v)
    end
    return new_params
 end

This gave me my desired result

回答1:

arr = x= [{:shipping_id=>2, :fsn=>"ab"}, 
{:shipping_id=>3, :fsn=>"abc"}, {:shipping_id=>2, :fsn=>"abcd"}, 
{:shipping_id=>4, :fsn=>"abx"}, {:shipping_id=>3, :fsn=>"abb"}]
@h = {}
arr.group_by {|x| x[:shipping_id]==2 }[true].inject({}) do |mem,i|
   i.each{|k,v| mem[k] =  [v] << mem[k] ; @h = mem}
end
p @h #=> {:shipping_id=>[2, 2], :fsn=>["abcd", "ab"]}

回答2:

You could do:

ret = Hash[x.group_by {|e| e[:shipping_id]}.map {|e| [e.first, e.last.map {|t| t[:fsn]}]}]

and then, if you need only the ones for shipping_id = 2

> ret[2]
=> ["ab", "abcd"]

回答3:

Edited:

>> z = x.group_by {|y| y[:shipping_id] }
#=> {2=>[{:shipping_id=>2, :fsn=>"ab"}, {:shipping_id=>2, :fsn=>"abcd"}], 3=>[{:shipping_id=>3, :fsn=>"abc"}, {:shipping_id=>3, :fsn=>"abb"}], 4=>[{:shipping_id=>4, :fsn=>"abx"}]}

>> Hash[z.map {|k, v| Array[[k]*v.count, v] }]
#=> {[2, 2]=>[{:shipping_id=>2, :fsn=>"ab"}, {:shipping_id=>2, :fsn=>"abcd"}], [3, 3]=>[{:shipping_id=>3, :fsn=>"abc"}, {:shipping_id=>3, :fsn=>"abb"}], [4]=>[{:shipping_id=>4, :fsn=>"abx"}]}

Not exactly what you need, still leave it here in case you find it useful somehow.

来源：https://stackoverflow.com/questions/16194778/grouping-via-an-element-in-hash