Benchmarking using semi-unnatural Array methods (#rotate and #drop) against the more natural Set difference.

results

Rehearsal ----------------------------------------------------------------
array: rotating and dropping   0.050000   0.000000   0.050000 (  0.055791)
set: difference                8.480000   0.020000   8.500000 (  8.500697)
set: dup and delete            8.890000   0.020000   8.910000 (  8.908871)
------------------------------------------------------ total: 17.460000sec

                                   user     system      total        real
array: rotating and dropping   0.060000   0.000000   0.060000 (  0.056425)
set: difference                8.830000   0.010000   8.840000 (  8.842558)
set: dup and delete            8.940000   0.030000   8.970000 (  8.969234)

set-vs-array-partitioning.rb

require 'benchmark'
require 'set'

LIMIT = 5_000
WORDS = File.foreach('/usr/share/dict/words').lazy.map(&:chomp).take(LIMIT).to_a

Benchmark.bmbm do |x|
  x.report("array: rotating and dropping") do
    partitions = WORDS

    partitions.each_with_index do |part, i|
      others = partitions.rotate(i).drop(1)
    end
  end

  x.report("set: difference") do
    partitions = Set.new(WORDS)

    partitions.each do |part|
      others = partitions - Set.new([part])
    end
  end

  x.report("set: dup and delete") do
    partitions = Set.new(WORDS)

    partitions.each do |part|
      others = partitions.dup.delete(part)
    end
  end
end