Sort hash by key, return hash in Ruby

Question

Would this be the best way to sort a hash and return Hash object (instead of Array):

h = {"a"=>1, "c"=>3, "b"=>2, "d"=>4}
# => {"a"=>1, "c"=>3, "b"=>2, "d"=>4}

Hash[h.sort]
# => {"a"=>1, "b"=>2, "c"=>3, "d"=>4}

Answer 1

In Ruby 2.1 it is simple:

h.sort.to_h

Answer 2

Note: Ruby >= 1.9.2 has an order-preserving hash: the order keys are inserted will be the order they are enumerated. The below applies to older versions or to backward-compatible code.

There is no concept of a sorted hash. So no, what you're doing isn't right.

If you want it sorted for display, return a string:

"{" + h.sort.map{|k,v| "#{k.inspect}=>#{v.inspect}"}.join(", ") + "}"

or, if you want the keys in order:

h.keys.sort

or, if you want to access the elements in order:

h.sort.map do |key,value|
  # keys will arrive in order to this block, with their associated value.
end

but in summary, it makes no sense to talk about a sorted hash. From the docs, "The order in which you traverse a hash by either key or value may seem arbitrary, and will generally not be in the insertion order." So inserting keys in a specific order into the hash won't help.

Answer 3

I've always used sort_by. You need to wrap the #sort_by output with Hash[] to make it output a hash, otherwise it outputs an array of arrays. Alternatively, to accomplish this you can run the #to_h method on the array of tuples to convert them to a k=>v structure (hash).

hsh ={"a" => 1000, "b" => 10, "c" => 200000}
Hash[hsh.sort_by{|k,v| v}] #or hsh.sort_by{|k,v| v}.to_h

There is a similar question in "How to sort a Ruby Hash by number value?".

Answer 4

You gave the best answer to yourself in the OP: Hash[h.sort] If you crave for more possibilities, here is in-place modification of the original hash to make it sorted:

h.keys.sort.each { |k| h[k] = h.delete k }

Answer 5

No, it is not (Ruby 1.9.x)

require 'benchmark'

h = {"a"=>1, "c"=>3, "b"=>2, "d"=>4}
many = 100_000

Benchmark.bm do |b|
  GC.start

  b.report("hash sort") do
    many.times do
      Hash[h.sort]
    end
  end

  GC.start

  b.report("keys sort") do
    many.times do
      nh = {}
      h.keys.sort.each do |k|
        nh[k] = h[k]
      end
    end
  end
end

       user     system      total        real
hash sort  0.400000   0.000000   0.400000 (  0.405588)
keys sort  0.250000   0.010000   0.260000 (  0.260303)

For big hashes difference will grow up to 10x and more

Answer 6

Sort hash by key, return hash in Ruby

With destructuring and Hash#sort

hash.sort { |(ak, _), (bk, _)| ak <=> bk }.to_h

Enumerable#sort_by

hash.sort_by { |k, v| k }.to_h

Hash#sort with default behaviour

h = { "b" => 2, "c" => 1, "a" => 3  }
h.sort         # e.g. ["a", 20] <=> ["b", 30]
hash.sort.to_h #=> { "a" => 3, "b" => 2, "c" => 1 }

Note: < Ruby 2.1

array = [["key", "value"]] 
hash  = Hash[array]
hash #=> {"key"=>"value"}

Note: > Ruby 2.1

[["key", "value"]].to_h #=> {"key"=>"value"}

Answer 7

ActiveSupport::OrderedHash is another option if you don't want to use ruby 1.9.2 or roll your own workarounds.

Answer 8

@ordered = {}
@unordered.keys.sort.each do |key|
  @ordered[key] = @unordered[key]
end

Answer 9

I had the same problem ( I had to sort my equipments by their name ) and i solved like this:

<% @equipments.sort.each do |name, quantity| %>
...
<% end %>

@equipments is a hash that I build on my model and return on my controller. If you call .sort it will sort the hash based on it's key value.

Answer 10

I borrowed Boris Stitnicky's inspired solution to patch an in-place sort! method into Hash:

def sort!
  keys.sort!.each { |k| store k, delete(k) }
  self
end

Answer 11

I liked the solution in the earlier post.

I made a mini-class, called it class AlphabeticalHash. It also has a method called ap, which accepts one argument, a Hash, as input: ap variable. Akin to pp (pp variable)

But it will (try and) print in alphabetical list (its keys). Dunno if anyone else wants to use this, it's available as a gem, you can install it as such: gem install alphabetical_hash

For me, this is simple enough. If others need more functionality, let me know, I'll include it into the gem.

EDIT: Credit goes to Peter, who gave me the idea. :)