Finding fastest way to compare 2 arrays...

compare_arrays.rb

require 'benchmark'
require 'set'

a = ["a","b","c","d"]
b = ["b","d"]

Benchmark.bm do |x|
	x.report do
		(a.inject(0) {|s,i| s += b.include?(i)?1:0 } == b.size)
	end
	x.report do
		(a & b).count == b.size
	end
	x.report do
		Set[b].subset?(a.to_set)
	end
	x.report do
		(b - a).empty?
	end
	x.report do
		b.all? { |o| a.include? o }
	end	
end


Results...

       user     system      total        real
   0.000000   0.000000   0.000000 (  0.000034)
   0.000000   0.000000   0.000000 (  0.000019)
   0.000000   0.000000   0.000000 (  0.000131)
   0.000000   0.000000   0.000000 (  0.000010)
   0.000000   0.000000   0.000000 (  0.000008)