Set of deep iteration helpers
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This small mixin allows the deep iteration / mapping of Enumerables instances.

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Adopted to be used with hashes/arrays. It is not intended to be used with large objects.


require 'iteraptor'

Blog post with detailed API documentation.

Iteraptor is intended to be used for iteration of complex nested structures. The yielder is being called with two parameters: “current key” and “current value.” The key is an index (converted to string for convenience) of an element for any Enumerable save for Hash.

Nested Enumerables are called with a compound key, represented as a “breadcrumb,” which is a path to current key, joined with Iteraptor::DELIMITER constant. The latter is just a dot in current release.


Boring (for users who are too conservative)

enum = [{foo: {bar: [:baz, 42]}}, [:foo, {bar: {baz: 42}}]].random

— enum.iteraptor.each(**params, ->(full_key, value))
—**params, ->(full_key, (key, value)))
—*filters, **params, ->(full_key, value))
— enum.iteraptor.reject(*filters, **params, ->(full_key, value))
— enum.iteraptor.compact(**params)
— enum.iteraptor.flat_map(**params, ->(full_key, value))
— enum.iteraptor.flatten(**params, ->(full_key, value))
— enum.iteraptor.collect(**params, ->(full_key, value))

Direct 🐒 patching in 🇪🇸

  • cada (sp. each) iterates through all the levels of the nested Enumerable, yielding parent, element tuple; parent is returned as a delimiter-joined string
  • mapa (sp. map) iterates all the elements, yielding parent, (key, value); the mapper should return either [key, value] array or nil to remove this element;
    • NB this method always maps to Hash, to map to Array use plana_mapa
    • NB this method will raise if the returned value is neither [key, value] tuple nor nil
  • plana_mapa iterates yielding key, value, maps to the yielded value, whatever it is; nils are not treated in some special way
  • aplanar (sp. flatten) the analogue of Array#flatten, but flattens the deep enumerable into Hash instance
  • recoger (sp. harvest, collect) the opposite to aplanar, it builds the nested structure out of flattened hash
  • segar (sp. yield), alias escoger (sp. select) allows to filter and collect elelements
  • rechazar (sp. reject) allows to filter out and collect elelements
  • compactar (sp. compact), allows to filter out all nils

Words are cheap, show me the code

require 'iteraptor'
#⇒ true

▶ hash = {company: {name: "Me", currencies: ["A", "B", "C"],
▷         password: "12345678",
▷         details: {another_password: "QWERTYUI"}}}
#⇒ {:company=>{:name=>"Me", :currencies=>["A", "B", "C"],
#              :password=>"12345678",
#              :details=>{:another_password=>"QWERTYUI"}}}

▶ hash.segar(/password/i) { "*" * 8 }
#⇒ {"company"=>{"password"=>"********",
#   "details"=>{"another_password"=>"********"}}}

▶ hash.segar(/password/i) { |*args| puts args.inspect }
["company.password", "12345678"]
["company.details.another_password", "QWERTYUI"]
#⇒ {"company"=>{"password"=>nil, "details"=>{"another_password"=>nil}}}

▶ hash.rechazar(/password/)
#⇒ {"company"=>{"name"=>"Me", "currencies"=>["A", "B", "C"]}}

▶ hash.aplanar
#⇒ {""=>"Me",
#   "company.currencies.0"=>"A",
#   "company.currencies.1"=>"B",
#   "company.currencies.2"=>"C",
#   "company.password"=>"12345678",
#   "company.details.another_password"=>"QWERTYUI"}

▶ hash.aplanar.recoger
#⇒ {"company"=>{"name"=>"Me", "currencies"=>["A", "B", "C"],
#   "password"=>"12345678",
#   "details"=>{"another_password"=>"QWERTYUI"}}}

▶ hash.aplanar.recoger(symbolize_keys: true)
#⇒ {:company=>{:name=>"Me", :currencies=>["A", "B", "C"],
#   :password=>"12345678",
#   :details=>{:another_password=>"QWERTYUI"}}}


Iteraptor#cada iterates all the Enumerable elements, recursively. As it meets the Enumerable, it yields it and then iterates items through.

λ = ->(parent, element) { puts "#{parent} » #{element.inspect}" }

[:a, b: {c: 42}].cada &λ
#⇒ 0 » :a
#⇒ 1 » {:b=>{:c=>42}}
#⇒ 1.b » {:c=>42}
#⇒ 1.b.c » 42

{a: 42, b: [:c, :d]}.cada &λ
#⇒ a » 42
#⇒ b » [:c, :d]
#⇒ b.0 » :c
#⇒ b.1 » :d


Mapper function should return a pair [k, v] or nil when called from hash, or just a value when called from an array. E. g., deep hash filtering:

▶ hash = {a: true, b: {c: '', d: 42}, e: ''}
#⇒ {:a=>true, :b=>{:c=>"", :d=>42}, :e=>""}
▶ hash.mapa { |parent, (k, v)| v == '' ? nil : [k, v] }
#⇒ {:a=>true, :b=>{:d=>42}}

This is not quite convenient, but I currently have no idea how to help the consumer to decide what to return, besides analyzing the arguments, received by code block. That is because internally both Hash and Array are iterated as Enumerables.


Find and report all empty values:

▶ hash = {a: true, b: {c: '', d: 42}, e: ''}
#⇒ {:a=>true, :b=>{:c=>"", :d=>42}, :e=>""}
▶ hash.cada { |k, v| puts "#{k} has an empty value" if v == '' }
#⇒ b.c has an empty value
#⇒ e has an empty value

Filter keys, that meet a condition:

In the example below we yield all keys, that matches the regexp given as parameter.

▶ hash.segar(/[abc]/) do |parent, elem|
▷   puts "Parent: #{parent.inspect}, Element: #{elem.inspect}"end
# Parent: "a", Element: true
# Parent: "b", Element: {:c=>"", :d=>42}
# Parent: "b.c", Element: ""
# Parent: "b.d", Element: 42

#⇒ {"a"=>true, "b"=>{:c=>"", :d=>42}, "b.c"=>"", "b.d"=>42}

Change all empty values in a hash to 'N/A':

▶ hash = {a: true, b: {c: '', d: 42}, e: ''}
#⇒ {:a=>true, :b=>{:c=>"", :d=>42}, :e=>""}
▶ hash.mapa { |parent, (k, v)| [k, v == '' ? v = 'N/A' : v] }
#⇒ {:a=>true, :b=>{:c=>"N/A", :d=>42}, :e=>"N/A"}

Flatten the deeply nested hash:

▶ hash = {a: true, b: {c: '', d: 42}, e: ''}
#⇒ {:a=>true, :b=>{:c=>"", :d=>42}, :e=>""}
▶ hash.aplanar(delimiter: '_', symbolize_keys: true)
#⇒ {:a=>true, :b_c=>"", :b_d=>42, :e=>""}


Add this line to your application's Gemfile:

gem 'iteraptor'

And then execute:

$ bundle

Or install it yourself as:

$ gem install iteraptor


  • 0.6.0 — experimental support for full_parent: true param
  • 0.5.0 — rechazar and escoger
  • 0.4.0 — aplanar and plana_mapa


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at[USERNAME]/iteraptor. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.