Merge values in a Hash

Question

nodes = {
  :node1 => { 
    :inherits => nil, 
    :variables => { :foo => 1, :bar => 2 } 
  },
  :node2 => { 
    :inherits => :node1, 
    :variables => { :foo => 9, :baz => 4 } 
  }
}

I've been trying to understand how to return a new nodes hash where each node's :variables hash is merged with :variables from the node specified in :inheritance. In other words, node1 would be left as is while node2 to end up with :variabes => { :foo => 9, :bar => 2, :baz => 4 }

I've been swimming through docs involving Enumerable#inject, Hash#merge with a block, and more and figure it's time to ask for help.

UPDATE:

Figured I'd provide an update. This code is certainly not the solution but it might be heading in the right direction...

nodes = {
  :node1 => { :inherits => nil, :variables => { :foo => 1, :bar => 2 } },
  :node2 => { :inherits => :node1, :variables => { :foo => 9, :baz => 4 } }
}

new = nodes.inject({}) do |result, (k, v)|
  result.merge k => v.merge({ :variables => { :a => 6, :b => 7 } })
end

returns

{:node2=>{:inherits=>:node1, :variables=>{:a=>6, :b=>7}}, :node1=>{:inherits=>nil, :variables=>{:a=>6, :b=>7}}}

So that v.merge is not working as intended...

score 1 · Answer 1 · answered Oct 07 '12 at 18:49

1

You want Hash#merge:

merged_variables = nodes[:node1][:variables].merge(nodes[:node2][:variables])

answered Oct 07 '12 at 18:49

user229044

232,980
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won't that produce a node with :foo = 1 ? – Dmitri Oct 07 '12 at 18:55
No, it won't: `{:foo=>9, :bar=>2, :baz=>4}` – user229044 Oct 07 '12 at 18:59
Thank you. This may be a bit too specific as I'm trying to return a new nodes hash with each node's :variables merged as needed (according to inheritance). I'll update my original question to reflect this. – user1727142 Oct 07 '12 at 19:08

score 1 · Answer 2 · answered Oct 07 '12 at 18:52

1

nodes[:node2][:variables].replace(
  nodes[:node1][:variables]
  .merge(nodes[:node2][:variables])
)

answered Oct 07 '12 at 18:52

sawa

165,429
45
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381

Andrew Haines · Accepted Answer · 2012-10-07T20:00:02.610

0

merged_nodes = {}

nodes.each do |name, node|
  merged_nodes[name] = node.dup
  merged_nodes[name][:variables] = if node[:inherits]
    nodes[node[:inherits]][:variables].merge node[:variables]
  else
    node[:variables].dup
  end
end

will give you

{
  :node1=>{:inherits=>nil, :variables=>{:foo=>1, :bar=>2}},
  :node2=>{:inherits=>:node1, :variables=>{:foo=>9, :bar=>2, :baz=>4}}
}

but it won't handle deeper nesting i.e. if :node3 then inherits :node2... if you need anything as complicated as that, this hash-based approach is going to get pretty clunky.

edited Oct 07 '12 at 20:00

answered Oct 07 '12 at 19:53

Andrew Haines

6,574
21
34

Kept digging into this and came up with the following: `new = nodes.inject({}) do |result, (name, node)| vars = node[:inherits].nil? ? node[:variables] : nodes[node[:inherits]][:variables] result.merge name => node.merge(:variables => node[:variables].merge(vars)) end` – user1727142 Oct 07 '12 at 22:47

score 0 · Answer 4 · answered Oct 07 '12 at 20:43

A little bit shorter by merging in place:

nodes[:node2][:variables].merge!(nodes[:node1][:variables])

nodes #=> {:node1=>{:inherits=>nil, :variables=>{:foo=>1, :bar=>2}},
      #    :node2=>{:inherits=>:node1, :variables=>{:foo=>1, :baz=>4, :bar=>2}}}

score 0 · Answer 5 · answered Oct 08 '12 at 07:44

new = {}
nodes.each do |e, v|
    v.each do |attribute, value|
        if attribute == :inherits
            new[e] = value.nil? ? v : nodes[value][:variables].merge( v[:variables] )
        end
    end
end

p new  #=> {:node1=>{:inherits=>nil, :variables=>{:foo=>1, :bar=>2}}, :node2=>{:foo=>9, :bar=>2, :baz=>4}}

Merge values in a Hash

5 Answers5