What is the fastest way to sort a Hash?

Question

People often ask what is the best way to sort a hash, but then they don\'t ask the needed follow-up question about what is the fastest way, which really determ

Answer 1

What is the fastest way to sort a Hash?

require 'fruity'

HASH = Hash[('a'..'z').to_a.shuffle.map{ |k| [k, 1] }]

def sort_hash1(h)
  h.sort.to_h
end

def sort_hash2(h)
  Hash[h.sort]
end

def sort_hash3(h)
  Hash[h.sort_by{ |k, v| k }]
end

def sort_keys(h)
  keys = h.keys.sort
  Hash[keys.zip(h.values_at(*keys))]
end

puts "Running on Ruby v#{ RUBY_VERSION }"
puts

compare do
  do_sort_hash1 { sort_hash1(HASH) } if [].respond_to?(:to_h)
  do_sort_hash2 { sort_hash2(HASH) }
  do_sort_hash3 { sort_hash3(HASH) }
  do_sort_keys { sort_keys(HASH) }
end

Running the above code on a Mac OS laptop results in the following output:

# >> Running on Ruby v2.2.2
# >> 
# >> Running each test 256 times. Test will take about 1 second.
# >> do_sort_keys is faster than do_sort_hash3 by 39.99999999999999% ± 10.0%
# >> do_sort_hash3 is faster than do_sort_hash1 by 1.9x ± 0.1
# >> do_sort_hash1 is similar to do_sort_hash2

And:

# >> Running on Ruby v1.9.3
# >> 
# >> Running each test 256 times. Test will take about 1 second.
# >> do_sort_keys is faster than do_sort_hash3 by 19.999999999999996% ± 10.0%
# >> do_sort_hash3 is faster than do_sort_hash2 by 4x ± 0.1

---

Doubling the hash size:

HASH = Hash[[*('a'..'z'), *('A'..'Z')].shuffle.map{ |k| [k, 1] }]

Results in:

# >> Running on Ruby v2.2.2
# >> 
# >> Running each test 128 times. Test will take about 1 second.
# >> do_sort_keys is faster than do_sort_hash3 by 50.0% ± 10.0%
# >> do_sort_hash3 is faster than do_sort_hash1 by 2.2x ± 0.1
# >> do_sort_hash1 is similar to do_sort_hash2

And:

# >> Running on Ruby v1.9.3
# >> 
# >> Running each test 128 times. Test will take about 1 second.
# >> do_sort_keys is faster than do_sort_hash3 by 30.000000000000004% ± 10.0%
# >> do_sort_hash3 is faster than do_sort_hash2 by 4x ± 0.1

---

The values will change depending on the hardware, but the relative results shouldn't change.

Fruity was chosen over using the built-in Benchmark class for simplicity.

This was prompted by "Sort hash by key, return hash in Ruby".