How to elegantly rename all keys in a hash in Ruby? [duplicate]

Answer 1

ages = { "Bruce" => 32, "Clark" => 28 }
mappings = {"Bruce" => "Bruce Wayne", "Clark" => "Clark Kent"}
ages = mappings.inject({}) {|memo, mapping| memo[mapping[1]] = ages[mapping[0]]; memo}
puts ages.inspect

Answer 2

If the mapping Hash will be smaller than the data Hash then iterate on mappings instead. This is useful for renaming a few fields in a large Hash:

class Hash
  def rekey(h)
    dup.rekey! h
  end

  def rekey!(h)
    h.each { |k, newk| store(newk, delete(k)) if has_key? k }
    self
  end
end

ages = { "Bruce" => 32, "Clark" => 28, "John" => 36 }
mappings = {"Bruce" => "Bruce Wayne", "Clark" => "Clark Kent"}
p ages.rekey! mappings

Answer 3

The Facets gem provides a rekey method that does exactly what you're wanting.

As long as you're okay with a dependency on the Facets gem, you can pass a hash of mappings to rekey and it will return a new hash with the new keys:

require 'facets/hash/rekey'
ages = { "Bruce" => 32, "Clark" => 28 }
mappings = {"Bruce" => "Bruce Wayne", "Clark" => "Clark Kent"}
ages.rekey(mappings)
=> {"Bruce Wayne"=>32, "Clark Kent"=>28}

If you want to modify ages hash in place, you can use the rekey! version:

ages.rekey!(mappings)
ages
=> {"Bruce Wayne"=>32, "Clark Kent"=>28}

Answer 4

There's the under-utilized each_with_object method in Ruby as well:

ages = { "Bruce" => 32, "Clark" => 28 }
mappings = { "Bruce" => "Bruce Wayne", "Clark" => "Clark Kent" }

ages.each_with_object({}) { |(k, v), memo| memo[mappings[k]] = v }

Answer 5

You may wish to use Object#tap to avoid the need to return ages after the keys have been modified:

ages = { "Bruce" => 32, "Clark" => 28 }
mappings = {"Bruce" => "Bruce Wayne", "Clark" => "Clark Kent"}

ages.tap {|h| h.keys.each {|k| (h[mappings[k]] = h.delete(k)) if mappings.key?(k)}}
  #=> {"Bruce Wayne"=>32, "Clark Kent"=>28}