Remove duplicates benchmark

Benchmark

require 'benchmark'

ary = 1000.times.collect { rand(2000) }

Benchmark.bm(10) do |x|
  x.report { ary.select { |e| ary.count(e) > 1 }.uniq }
  x.report { ary.group_by {|e| e}.select { |k, v| v.size > 1 }.map(&:first) }
  x.report { ary.uniq.select { |i| ary.count(i) > 1 } }
  x.report { ary.uniq.select { |i| ary.delete_at(ary.index(i)) && ary.delete_at(ary.index(i) || ary.length) } }
  x.report { ary.uniq.delete_if { |i| ary.one? { |elm| elm == i } } }
end

results

                user     system      total        real
            0.050000   0.000000   0.050000 (  0.050655)
            0.000000   0.000000   0.000000 (  0.001314)
            0.030000   0.000000   0.030000 (  0.037768)
            0.020000   0.000000   0.020000 (  0.017854)
            0.000000   0.000000   0.000000 (  0.000200)