#inject and slowness
I've often heard the Ruby injection method criticized as "slow". Since I love this feature and I see equivalents in other languages, I am curious if this is just a slow way of doing Ruby, or if this is inherently a slow way of doing things (eg should be avoided for non-small sets)?
inject
is similar to fold
and can be very efficient in other languages, fold_left
in particular since it is tail-recursive.
This is mostly an implementation issue, but it gives you a good idea of the comparison:
$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]
$ ruby exp/each_v_inject.rb
Rehearsal -----------------------------------------------------
loop 0.000000 0.000000 0.000000 ( 0.000178)
fixnums each 0.790000 0.280000 1.070000 ( 1.078589)
fixnums each add 1.010000 0.290000 1.300000 ( 1.297733)
Enumerable#inject 1.900000 0.430000 2.330000 ( 2.330083)
-------------------------------------------- total: 4.700000sec
user system total real
loop 0.000000 0.000000 0.000000 ( 0.000178)
fixnums each 0.760000 0.300000 1.060000 ( 1.079252)
fixnums each add 1.030000 0.280000 1.310000 ( 1.305888)
Enumerable#inject 1.850000 0.490000 2.340000 ( 2.340341)
exp / each_v_inject.rb
require 'benchmark'
total = (ENV['TOTAL'] || 1_000).to_i
fixnums = Array.new(total) {|x| x}
Benchmark.bmbm do |x|
x.report("loop") do
total.times { }
end
x.report("fixnums each") do
total.times do |i|
fixnums.each {|x| x}
end
end
x.report("fixnums each add") do
total.times do |i|
v = 0
fixnums.each {|x| v += x}
end
end
x.report("Enumerable#inject") do
total.times do |i|
fixnums.inject(0) {|a,x| a + x }
end
end
end
So, yes, it's slow, but as improvements happen in the implementation, it should become a non-problem. As far as what it does, there is nothing that requires it to be slower.
each_with_object
may be faster than inject
if you mutate an existing object rather than creating a new object in every block.