Comparison of Enumerable#graph with to_h

[denispeplin]

Hi!

I compaired Enumerable#graph from facets with Enumerable.to_h from Ruby.

require 'facets'
require 'benchmark'

k = 10_000_000
numbers  = (1..k)

Benchmark.bmbm do |x|
  x.report(:graph) { numbers.graph { |n| [n, n*n] } }
  x.report(:map)   { numbers.map   { |n| [n, n*n] }.to_h }
end

Rehearsal -----------------------------------------
graph   9.780000   0.150000   9.930000 (  9.949591)
map    10.770000   0.160000  10.930000 ( 10.934696)
------------------------------- total: 20.860000sec

            user     system      total        real
graph   8.530000   0.000000   8.530000 (  8.527301)
map     8.130000   0.000000   8.130000 (  8.132008)

Results are comparable. Second version should have a bigger memory footprint, so I compared them too:

# graph.rb
require 'facets'

k = 10_000_000
numbers  = (1..k)

numbers.graph { |n| [n, n*n] }

ruby-prof graph.rb
Measure Mode: memory
Total: 581817.523438

# to_h.rb
k = 10_000_000
numbers  = (1..k)

numbers.map   { |n| [n, n*n] }.to_h

ruby-prof to_h.rb 
Measure Mode: memory
Total: 649572.859375

Yes, the memory footprint is larger as expected.

Implementations may give different results on a different input, so I started to explore them, and found, that this line: https://github.com/rubyworks/facets/blob/master/lib/core/facets/enumerable/graph.rb#L29 is not covered by tests. This might be an issue.