Turning a Hash of Arrays into an Array of Hashes in Ruby

Convert hash to array of hashes

Leveraging Array#transpose and Array#to_h

keys = list.keys
list.values.transpose.map { |v| keys.zip(v).to_h }

Turning a Hash of Arrays into an Array of Hashes in Ruby

This solution works with arbitrary numbers of values (val1, val2...valN):

{:a => ["val1", "val2"], :b => ["valb1", "valb2"]}.inject([]){|a, (k,vs)| 
  vs.each_with_index{|v,i| (a[i] ||= {})[k] = v} 
  a
}
# => [{:a=>"val1", :b=>"valb1"}, {:a=>"val2", :b=>"valb2"}]

[{:a=>"val1", :b=>"valb1"}, {:a=>"val2", :b=>"valb2"}].inject({}){|a, h| 
  h.each_pair{|k,v| (a[k] ||= []) << v}
  a
}
# => {:a=>["val1", "val2"], :b=>["valb1", "valb2"]}

Merge hash of arrays into array of hashes

I suggest writing the code to permit arbitrary numbers of attributes. It's no more difficult than assuming there are two (:name and :surname), yet it provides greater flexibility, accommodating, for example, future changes to the number or naming of attributes:

def squish(h)
  keys = h.keys.map(&:to_s)
  h.values.transpose.map { |a| keys.zip(a).to_h }
end

h = { name:    ["John", "Jane", "Chris"],
      surname: ["Doe", "Doe", "Smith"],
      age:     [22, 34, 96]
    }    

squish(h)
  #=> [{"name"=>"John", "surname"=>"Doe", "age"=>22},
  #    {"name"=>"Jane", "surname"=>"Doe", "age"=>34},
  #    {"name"=>"Chris", "surname"=>"Smith", "age"=>96}] 

The steps for the example above are as follows:

b = h.keys
  #=> [:name, :surname, :age] 
keys = b.map(&:to_s)
  #=> ["name", "surname", "age"] 
c = h.values
  #=> [["John", "Jane", "Chris"], ["Doe", "Doe", "Smith"], [22, 34, 96]] 
d = c.transpose
  #=> [["John", "Doe", 22], ["Jane", "Doe", 34], ["Chris", "Smith", 96]] 
d.map { |a| keys.zip(a).to_h }
  #=> [{"name"=>"John", "surname"=>"Doe", "age"=>22},
  #    {"name"=>"Jane", "surname"=>"Doe", "age"=>34},
  #    {"name"=>"Chris", "surname"=>"Smith", "age"=>96}] 

In the last step the first value of b is passed to map's block and the block variable is assigned its value.

a = d.first
  #=> ["John", "Doe", 22] 
e = keys.zip(a)
  #=> [["name", "John"], ["surname", "Doe"], ["age", 22]] 
e.to_h
  #=> {"name"=>"John", "surname"=>"Doe", "age"=>22} 

The remaining calculations are similar.

transform array of arrays in array of hash

array = [
    [ 1, "name1" ],
    [ 2, "name2" ],
    [ 3, "name3" ],
    [ 4, "name4" ]
]
array.map { |e| ['id', 'name'].zip(e).to_h }
#⇒ [
#    {"id"=>1, "name"=>"name1"},
#    {"id"=>2, "name"=>"name2"},
#    {"id"=>3, "name"=>"name3"},
#    {"id"=>4, "name"=>"name4"}
# ]

The only interesting here is Enumerable#zip, that “merges” arrays.

Convert array of hashes to array

a=[{:code=>"404"}, {:code=>"302"}, {:code=>"200"}] 
puts a.map{|x|x.values}.flatten.inspect

output

["404", "302", "200"]

Convert array of hashes to single hash with values as keys

This should do what you want

countries.each_with_object({}) { |country, h| h[country[:country].to_sym] = country[:cost] }
 => {:england=>12.34, :scotland=>56.78}

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