Given N sets, returns the set of all elements which occur in only one of those sets

0_brief.txt

TheHodge: anyone got any suggestions on how to compare 
four arrays for unique elements
TheHodge: I want a count of the unique elements in each 
array, elements that don't appear in any of the other 
three
TheHodge: the four arrays could easily turn into 6 and 
then 8 as they are files in a directory

1_set_differences.rb

require 'set'

a = Set[1,2,3,4]
b = Set[2,3,4,5]
c = Set[3,4,5,6]
d = Set[4,5,6,7]

diff = a - (b | c | d)
puts diff.inspect # => #<Set: {1}>

diff = d - (b | c | a)
puts diff.inspect # => #<Set: {7}>

# What you need is the difference of given set A, against
# the Union of sets B, C and D

# This means you'll need to do some combinatorial stuff

all_sets = Set[a,b,c,d]

uniques = all_sets.collect do |s|
  others = all_sets.dup.delete(s)
  union = others.reduce(:|)
  diff = union ? s - union : nil
  diff
end.reduce(:|)

puts uniques.inspect # => #<Set: {1, 7}>
puts uniques.to_a.inspect # => [1, 7]

2_benchmarking.rb

require 'set'
require 'securerandom'

all_sets = Set[]

100.times do
  s = Set[]
  100.times do
    s.add(SecureRandom.hex(2))
  end
  all_sets.add(s)
end

uniques = all_sets.collect do |s|
  others = all_sets.dup.delete(s)
  union = others.reduce(:|)
  diff = union ? s - union : nil
  diff
end.reduce(:|)

uniques_count = uniques.to_a.count
puts "Generated #{uniques_count} unique hex strings across 100 sets (#{10_000 - uniques_count} were duplicated.)"