Array Merge (Union)

Question

I have two array I need to merge, and using the Union (|) operator is PAINFULLY slow.. are there any other ways to accomplish an array merge?

Also, the arrays are fi

Answer 1

Do you need the items to be in a specific order within the arrays? If not, you may want to check whether using Sets makes it faster.

Update

Adding to another answerer's code:

require "set"
require "benchmark"

a1 = []; a2 = []
[a1, a2].each do |a|
  1000000.times { a << rand(999999) }
end

s1, s2 = Set.new, Set.new

[s1, s2].each do |s|
  1000000.times { s << rand(999999) }
end

puts "Merge with pipe:"
puts Benchmark.measure { a1 | a2 }

puts "Merge with concat and uniq:"
puts Benchmark.measure { (a1 + a2).uniq }

puts "Concat only:"
puts Benchmark.measure { a1 + a2 }

puts "Uniq only:"
b = a1 + a2
puts Benchmark.measure { b.uniq }

puts "Using sets"
puts Benchmark.measure {s1 + s2}

puts "Starting with arrays, but using sets"
puts Benchmark.measure {s3, s4 = [a1, a2].map{|a| Set.new(a)} ; (s3 + s4)}

gives (for ruby 1.8.7 (2008-08-11 patchlevel 72) [universal-darwin10.0])

Merge with pipe:
  1.320000   0.040000   1.360000 (  1.349563)
Merge with concat and uniq:
  1.480000   0.030000   1.510000 (  1.512295)
Concat only:
  0.010000   0.000000   0.010000 (  0.019812)
Uniq only:
  1.460000   0.020000   1.480000 (  1.486857)
Using sets
  0.310000   0.010000   0.320000 (  0.321982)
Starting with arrays, but using sets
  2.340000   0.050000   2.390000 (  2.384066)

Suggests that sets may or may not be faster, depending on your circumstances (lots of merges or not many merges).