Issue #7793 has been updated by Thomas Sawyer.


An issue with the name is that "map" semantically means to create an Array, i.e.`ahash.map{ |k,v| ... }` produces an Array. So `map_keys` would make sense to mean `ahash.map_keys{ |k| ... }` and produce an Array too. `Hash#map_pair` would just a synonym for `#map`, just as `#each_pair` is just a synonym for `#each`.

Facets has long had `Hash#rekey` and `Hash#revalue` (and in-place forms `Hash#rekey!` and `Hash#revalue!`). These names are concise and do not suffer this semantic issue. Note Facets doesn't have a `#remap` method (though I suppose it could) because it has Enumerable#mash, and it's alias #graph, which can create a Hash from any Enumerable object.


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Feature #7793: New methods on Hash
https://bugs.ruby-lang.org/issues/7793#change-48695

* Author: Dominic Sisneros
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* Category: core
* Target version: next minor
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It would be nice to have the following methods added to hash

~~~ruby
h = { name: 'dominic', request: 'add the following methods', :why => 'convenience'}

h.map_v{|v| v.upcase}
#=> {:name=>"DOMINIC", :request=>"ADD THE FOLLOWING METHODS", :why=>"CONVENIENCE"}

h.map_k{|k| k.to_s}
#=> { "name"=> 'dominic', "request"=>"add the following methods', "why" => "convenience"}

h.map_kv{|k,v| [k.to_s, v.upcase]}
#=> { "name"=>"DOMINIC", "request"=>"ADD THE FOLLOWING METHODS", "why"=>"CONVENIENCE"}


class Hash

  def map_v
    reduce({}) do |result, array|
      k,v = array
      new_val = yield v
      result.merge( k => new_val)
    end
  end

  def map_k
    reduce({}) do |result, array|
      k,v = array
      new_k = yield k
      result.merge(new_k => v)
    end
  end

  def map_kv
    reduce({}) do |result, array|
      new_k,new_v = yield array
      result.merge(new_k => new_v)
    end
  end

end




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