Ruby quickly make an array out of part of a hash of hashes?

Question

Okay, so if I have a hash of hashes to represent books like this:

Books = 
{"Harry Potter" => {"Genre" => Fantasy, "Author" => "Rowling"},
 "Lord of the Rings" => {"Genre" => Fantasy, "Author" => "Tolkien"}
 ...
}

Is there any way that I could concisely get an array of all authors in the books hash? (If the same author is listed for multiple books, I would need their name in the array once for each book, so no need to worry about weeding out duplicates) For example, I would like to be able to use it in the following way:

list_authors(insert_expression_that_returns_array_of_authors_here)

Does anyone know how to make this kind of expression? Thanks very much in advance for any help received.

This also works: `books.to_s.scan(/\"Author\"\s*=>\s*\"(.+?)\"/).flatten`. Not recommending; just saying. — Cary Swoveland, Mar 04 '14 at 23:34

score 5 · Accepted Answer · answered Mar 04 '14 at 17:12

5

Get hash values, then extract authors from that values (arrayes of hashes) using Enumerable#map:

books = {
  "Harry Potter" => {"Genre" => "Fantasy", "Author" => "Rowling"},
  "Lord of the Rings" => {"Genre" => "Fantasy", "Author" => "Tolkien"}
}
authors = books.values.map { |h| h["Author"] }
# => ["Rowling", "Tolkien"]

answered Mar 04 '14 at 17:12

falsetru

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Fantastic. It never ceases to amaze me how supporting the community is. :D Answer works perfectly, thanks for the rapid reply! – user3380049 Mar 04 '14 at 18:22

score 4 · Answer 2 · answered Mar 04 '14 at 17:14

4

I'd do

Books = { 
           "Harry Potter" => {"Genre" => 'Fantasy', "Author" => "Rowling"},
           "Lord of the Rings" => {"Genre" => 'Fantasy', "Author" => "Tolkien"}
        }

authors = Books.map { |_,v| v["Author"] }
# => ["Rowling", "Tolkien"]

answered Mar 04 '14 at 17:14

Arup Rakshit

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Stacked-for-life · Answer 3 · 2014-03-04T18:30:43.753

0

I would do.

     Books = { 
       "Harry Potter" => {"Genre" => 'Fantasy', "Author" => "Rowling"},
       "Lord of the Rings" => {"Genre" => 'Fantasy', "Author" => "Tolkien"}
              }

     def list_authors(hash)
       authors = Array.new
       hash.each_value{|value| authors.push(value["Author"]) }
       return authors 
    end


     list_authors(Books)

edited Mar 04 '14 at 18:30

answered Mar 04 '14 at 18:16

Stacked-for-life

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Ruby quickly make an array out of part of a hash of hashes?

3 Answers3