bench.rb

require "benchmark"

def p_q_str_to_num(str)
  str =~ /^p(\d+)q(\d+)$/
  ($1+$2).to_i
end

arr = (1..100000).map {"p#{rand(1000)}q#{rand(1000)}"}

Benchmark.bmbm do |x|
  x.report("sort")    { arr.sort    { |x,y| p_q_str_to_num(x) <=> p_q_str_to_num(y) }  } 
  x.report("sort_by") { arr.sort_by { |id| id =~ /^p(\d+)q(\d+)$/; ($1+$2).to_i     }  } 
end

jruby-1.6.2

Rehearsal -------------------------------------------
sort      7.243000   0.000000   7.243000 (  7.036000)
sort_by   0.997000   0.000000   0.997000 (  0.997000)
---------------------------------- total: 8.240000sec

              user     system      total        real
sort      5.726000   0.000000   5.726000 (  5.726000)
sort_by   0.695000   0.000000   0.695000 (  0.695000)

rubinius 2.0.0dev

Rehearsal -------------------------------------------
sort     12.080000   0.010000  12.090000 ( 12.535100)
sort_by   1.120000   0.010000   1.130000 (  1.286980)
--------------------------------- total: 13.220000sec

              user     system      total        real
sort     10.890000   0.010000  10.900000 ( 10.938454)
sort_by   0.750000   0.010000   0.760000 (  0.823790)

Ruby 1.9.2-p290

Rehearsal -------------------------------------------
sort     12.040000   0.030000  12.070000 ( 12.116498)
sort_by   0.440000   0.000000   0.440000 (  0.438764)
--------------------------------- total: 12.510000sec

              user     system      total        real
sort     10.020000   0.030000  10.050000 ( 10.054058)
sort_by   0.410000   0.000000   0.410000 (  0.416572)