Sorting Array of Hashes (Ruby)

Question

If I have a method that adds two arrays of hashes together and then sorts them based on a specified order, is it possible to sort it again based on a second specified order?

If I my method looks something like:

def all_pets

     #set order by fur color
     order = ['Black', 'Orange', 'Golden', 'Mixed']

     all_pets = dogs + cats #two arrays being added together

     all_pets.sort_by {|r| order.index(r[:fur_color])}

end

My output currently looks like:

  [{:name=>"Kitty", :fur_color=>"Black"} #cat,
  {:name=>"Fido", :fur_color=>"Black"} #dog, 
  {:name=>"Whiskers", :fur_color=>"Black"} #cat, 
  {:name=>"Buttons", :fur_color=>"Orange"} #cat, 
  {:name=>"Mr.Cat", :fur_color=>"Golden"} #cat, 
  {:name=>"Sparky", :fur_color=>"Golden"} #dog,
  {:name=>"Max", :fur_color=>"Mixed"} #dog]

This is great so far, I have the animals sorted by fur color exactly how I want, is it possible to then sort so cats will always come after dogs?

The two arrays being added have the exact same attributes (name and fur color), so I'm not sure how to order them by fur color first, and animal type second.

Since both arrays have the same attributes, and no animal type attribute, would it be possible to do something that puts all hashes that came from the array cat to come after the hashes from array dog after they've been sorted by fur color?

So my goal output would be:

  [{:name=>"Fido", :fur_color=>"Black"} #dog,
   {:name=>"Kitty", :fur_color=>"Black"} #cat, 
  {:name=>"Whiskers", :fur_color=>"Black"} #cat, 
  {:name=>"Buttons", :fur_color=>"Orange"} #cat, 
  {:name=>"Sparky", :fur_color=>"Golden"} #dog,
  {:name=>"Mr.Cat", :fur_color=>"Golden"} #cat, 
  {:name=>"Max", :fur_color=>"Mixed"} #dog]

Thanks!

When you say you want cats to come before dogs, do you mean you want all all black dogs, then all orange dogs, then all golden dogs, then all mixed dogs, then all black cats, then all orange cats, then all golden cats, then all mixed cats? — Piccolo, Jul 26 '18 at 16:23
@Piccolo Edited my post, hopefully its a bit more clear. Thanks! — kkir, Jul 26 '18 at 16:36
Possible duplicate of [How to sort an array of hashes in ruby](https://stackoverflow.com/questions/5483889/how-to-sort-an-array-of-hashes-in-ruby) — jedi, Jul 26 '18 at 20:25
@jedi, the question you reference is concerned with sorting an array of hashes on a single key's value. — Cary Swoveland, Jul 27 '18 at 02:32
kkir, you don't need the reference to Ruby in the title; that's taken care of by your Ruby tag. — Cary Swoveland, Aug 07 '18 at 06:16

Aleksei Matiushkin · Accepted Answer · 2018-07-26T16:28:15.760

3

Just pass an array to sort_by:

all_pets.sort_by {|r| [order.index(r[:fur_color]), r[:name]] }

The above will sort by the color and by the name inside the same color.

all_pets.sort_by do |r|
  [
    order.index(r[:fur_color]),
    cats.map { |c| c[:name] }.include?(r[:name])
    # or cats.include?(r)
  ]
end

The latter will put cats after dogs.

edited Jul 26 '18 at 16:28

answered Jul 26 '18 at 16:23

Aleksei Matiushkin

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@SergioTulentsev why not? I am into Erlang ideology nowadays, it explicitly says: fail fast! – Aleksei Matiushkin Jul 26 '18 at 16:28
When I read "put cats after dogs", my initial thought was ["give me a research team and 5 years"](https://xkcd.com/1425/). But the solution is trivial, turns out. :) – Sergio Tulentsev Jul 26 '18 at 16:37
@SergioTulentsev yeah, nested sorting is kinda easier than ML :) – Aleksei Matiushkin Jul 26 '18 at 16:41
Why would you use `cats.map { |c| c[:name] }.include?(r[:name])` instead of `cats.include?(r)`? The latter seems cleaner and I can't imagine any performance benefit – Piccolo Jul 26 '18 at 16:41
@Piccolo for the sake of example. I explicitly mentioned `cats.include?(r)` variant in a comment 1 line below. – Aleksei Matiushkin Jul 26 '18 at 16:42
Yeah I see that, but I'm just wondering why that isn't your default approach to this; it seems more elegant/readable – Piccolo Jul 26 '18 at 16:51
@Piccolo _for the sake of example_. I demonstrate an ability to build as complicated sorter as needed. – Aleksei Matiushkin Jul 26 '18 at 16:54

Cary Swoveland · Answer 2 · 2018-07-27T02:22:16.383

Here we can make use of the fact that, when used without a block, Enumerable#sort_by returns an enumerator.

COLOR_ORDER = ['Black', 'Orange', 'Golden', 'Mixed'].each_with_index.to_h
  #=> {"Black"=>0, "Orange"=>1, "Golden"=>2, "Mixed"=>3}

def sort_pets(pets)
  pets.sort_by.with_index { |pet, idx| [COLOR_ORDER[pet[:fur_color]], idx] }
end

dogs = [{ :name=>"Sparky",   :fur_color=>"Golden" },
        { :name=>"Max",      :fur_color=>"Mixed"  }, 
        { :name=>"Fido",     :fur_color=>"Black"  }]

cats = [{ :name=>"Kitty",    :fur_color=>"Black"  }, 
        { :name=>"Whiskers", :fur_color=>"Black"  }, 
        { :name=>"Buttons",  :fur_color=>"Orange" },
        { :name=>"Mr.Cat",   :fur_color=>"Golden" }]

sort_pets(dogs + cats)
  #=> [{:name=>"Fido",     :fur_color=>"Black "},
  #    {:name=>"Kitty",    :fur_color=>"Black" },
  #    {:name=>"Whiskers", :fur_color=>"Black" },
  #    {:name=>"Buttons",  :fur_color=>"Orange"},
  #    {:name=>"Sparky",   :fur_color=>"Golden"},
  #    {:name=>"Mr.Cat",   :fur_color=>"Golden"},
  #    {:name=>"Max",      :fur_color=>"Mixed" }]

Sorting Array of Hashes (Ruby)

2 Answers2