Group by and format array of hash values in ruby

Question

Hey I have an array of hash values as follows.

[{"group" => "1", "message" => "hey", "weight" => 1}, {"group" => "1", "message" 
 => "hey1", "weight" => 2}, {"group" => "2", "message" => "hey3", "weight" => 4}]

I want to group_by group and format it so that I get the following:

[{"group" => 1, "messages" => {"hey","hey1"}, "weights" => {1,2}}, {"group" => 2,
  "messages" => {"hey3"}, "weights" => {4}}]

Is there a nice ruby way to achieve this?

Edit: Now I have:

[
  {"group" => "1", "message" => {"hey" => "1"}},
  {"group" => "1", "message" => {"hey1" => "2"}}
]

I'd like to have

{"group" => "1", "messages" => {"hey1" => "1", "hey2" => "2"} }

You mean [{"group" => 1, "messages" => ["hey","hey1"], "weights" => [1,2]}? — steenslag
– steenslag, Commented Jun 20, 2012 at 19:45
You mean arrays of the messages and weights, right, assuming that they're both ordered the same? Personally, I'd just key off the group, and keep the message and weight as a complete object to avoid any confusion. — Dave Newton
– Dave Newton, Commented Jun 20, 2012 at 19:46
Duplicate of Merge array of hashes to get hash of arrays of values — Phrogz
– Phrogz, Commented Jun 20, 2012 at 19:57
Yeah I kept msg and weight as own object so now I have the following [{"group" => "1", "message" => {"hey" => "1"}}, {"group" => "1", "message" => {"hey1" => "2"}}] I'd like to have [{"group" => "1", "messages" => {"hey1" => "1", "hey2" => 2"}] — Emmanuel P
– Emmanuel P, Commented Jun 20, 2012 at 19:58
Your needs are rather underspecified. What do you want for [{a:1},{a:2}] or [{a:1},{b:2}] or [{a:{b:3}},{a:{b:3}}] or [{a:{b:3}},{a:{b:4}}]? — Phrogz
– Phrogz, Commented Jun 20, 2012 at 20:20

Phrogz · Accepted Answer · 2012-06-20 20:07:03Z

2

Based on your revised question:

groups = [
  {"group" => "1", "message" => {"hey" => "1"}},
  {"group" => "1", "message" => {"hey1" => "2"}}
]

merged = groups.inject do |h1,h2|
  h1.merge(h2) do |k,v1,v2|
    if v1==v2
      v1
    elsif v1.is_a?(Hash) && v2.is_a?(Hash)
      v1.merge(v2)
    else
      [*v1,*v2]
    end
  end
end

p merged
#=> {"group"=>"1", "message"=>{"hey"=>"1", "hey1"=>"2"}}

answered Jun 20, 2012 at 20:07

Phrogz

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Comments

alf · Accepted Answer · 2012-06-20 19:55:40Z

1

I think the output you want is:

[{"messages"=>["hey", "hey1"], "weights"=>[1, 2], "group"=>"1"}, {"messages"=>["hey3"], "weights"=>[4], "group"=>"2"}]

If this is the case, this code does what you want:

h.group_by { |item| item["group"] }.values.map do |item|
    item.inject({"messages" => [], "weights" => []}) do |result, subitem|
        result["group"] = subitem["group"]
        result["messages"] << subitem["message"]
        result["weights"] << subitem["weight"]
        result
    end
end

You should be able to improve it knowing more about your specific problem, but it should be a good starting point.

answered Jun 20, 2012 at 19:55

alf

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