Add benchmark for Array#new vs. Fixnum#times + map

[Drenmi]

When you need to map the result of a block invoked a fixed amount of times, you have an option between:

Array.new(n) { ... }

and:

n.times.map { ... }

The latter one is about 60% slower for n = 10, which goes down to around 40% for n > 1_000.

Note: logarithmic scale!

[nateberkopec]

How does this change with the number of elements?

[Drenmi]

@nateberkopec: It tapers off a bit, and stabilizes around 40% slower at 1_000 elements and up. Note: logarithmic scale!

[nateberkopec]

Thank you so much for the graph! I'm just getting started with this repo, so someone else should comment, but whenever there's an Array or Enumerable benchmark I'm always curious with how it scales with # of elements. You may want to add a comment explaining that this behaves pretty much the same way at 1 million elements as it does at 10.

[Drenmi]

No problems @nateberkopec. :-) Is a comment in the PR sufficient, or do you want me to add it to the README?

[nateberkopec]

shrug let's see what someone else thinks

[deniskorobicyn]

I vote for link to this PR in README.md.
This'll make info available for everyone, not only for people who reviewing PR's. Also, link will share that cool graph you have here:)

[JuanitoFatas]

I vote for link to this PR in README.md.

👍

@Drenmi Awesome graph 👏 👏 👏

[Drenmi]

@nateberkopec, @deniskorobicyn, @JuanitoFatas: Thanks for the kind words. 😃 I added the graph to the PR description, and linked to the PR from the README.

[Arcovion]

There's a faster way:

require 'benchmark/ips'

LIMIT = 9

def fastest
  [].fill(0, LIMIT, &:itself)
end

def fast
  Array.new(LIMIT, &:itself)
end

def slow
  (0...LIMIT).map(&:itself)
end

def slowest
  LIMIT.times.map(&:itself)
end

Benchmark.ips do |bm|
  bm.report('Array#fill') { fastest }
  bm.report('Array#new') { fast }
  bm.report('Range#map') { slow }
  bm.report('Fixnum#times') { slowest }
  bm.compare!
end

Calculating -------------------------------------
          Array#fill    81.773k i/100ms
           Array#new    72.230k i/100ms
           Range#map    60.548k i/100ms
        Fixnum#times    56.625k i/100ms
-------------------------------------------------
          Array#fill      1.507M (± 1.4%) i/s -      7.605M
           Array#new      1.191M (± 1.7%) i/s -      5.995M
           Range#map    992.912k (± 1.9%) i/s -      4.965M
        Fixnum#times    868.483k (± 0.9%) i/s -      4.360M

Comparison:
          Array#fill:  1506707.9 i/s
           Array#new:  1191006.1 i/s - 1.27x slower
           Range#map:   992912.3 i/s - 1.52x slower
        Fixnum#times:   868483.2 i/s - 1.73x slower

[avellable]

Let me add a reference to this.

@JuanitoFatas We can merge this.

[Drenmi]

Ping @JuanitoFatas. 😘

[ixti]

@Drenmi can you please add what @Arcovion said?