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Use a Schwartzian transform with custom sorting (#6342)

Merge pull request 6342
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parkr authored and jekyllbot committed Sep 2, 2017
1 parent 1a4f53d commit 6ce912e9573893babb6ca9b0e3aa1377f9804373
Showing with 133 additions and 11 deletions.
  1. +115 −0 benchmark/schwartzian_transform.rb
  2. +18 −11 lib/jekyll/filters.rb
@@ -0,0 +1,115 @@
#!/usr/bin/env ruby
# frozen_string_literal: true
#
# The Ruby documentation for #sort_by describes what's called a Schwartzian transform:
#
# > A more efficient technique is to cache the sort keys (modification times in this case)
# > before the sort. Perl users often call this approach a Schwartzian transform, after
# > Randal Schwartz. We construct a temporary array, where each element is an array
# > containing our sort key along with the filename. We sort this array, and then extract
# > the filename from the result.
# > This is exactly what sort_by does internally.
#
# The well-documented efficiency of sort_by is a good reason to use it. However, when a property
# does not exist on an item being sorted, it can cause issues (no nil's allowed!)
# In Jekyll::Filters#sort_input, we extract the property in each iteration of #sort,
# which is quite inefficient! How inefficient? This benchmark will tell you just how, and how much
# it can be improved by using the Schwartzian transform. Thanks, Randall!
require 'benchmark/ips'
require 'minitest'
require File.expand_path("../lib/jekyll", __dir__)
def site
@site ||= Jekyll::Site.new(
Jekyll.configuration("source" => File.expand_path("../docs", __dir__))
).tap(&:reset).tap(&:read)
end
def site_docs
site.collections["docs"].docs.dup
end
def sort_by_property_directly(docs, meta_key)
docs.sort! do |apple, orange|
apple_property = apple[meta_key]
orange_property = orange[meta_key]
if !apple_property.nil? && !orange_property.nil?
apple_property <=> orange_property
elsif !apple_property.nil? && orange_property.nil?
-1
elsif apple_property.nil? && !orange_property.nil?
1
else
apple <=> orange
end
end
end
def schwartzian_transform(docs, meta_key)
docs.collect! { |d|
[d[meta_key], d]
}.sort! { |apple, orange|
if !apple[0].nil? && !orange[0].nil?
apple.first <=> orange.first
elsif !apple[0].nil? && orange[0].nil?
-1
elsif apple[0].nil? && !orange[0].nil?
1
else
apple[-1] <=> orange[-1]
end
}.collect! { |d| d[-1] }
end
# Before we test efficiency, do they produce the same output?
class Correctness
include Minitest::Assertions
require "pp"
define_method :mu_pp, &:pretty_inspect
attr_accessor :assertions
def initialize(docs, property)
@assertions = 0
@docs = docs
@property = property
end
def assert!
assert sort_by_property_directly(@docs, @property).is_a?(Array), "sort_by_property_directly must return an array"
assert schwartzian_transform(@docs, @property).is_a?(Array), "schwartzian_transform must return an array"
assert_equal sort_by_property_directly(@docs, @property),
schwartzian_transform(@docs, @property)
puts "Yeah, ok, correctness all checks out for property #{@property.inspect}"
end
end
Correctness.new(site_docs, "redirect_from".freeze).assert!
Correctness.new(site_docs, "title".freeze).assert!
# First, test with a property only a handful of documents have.
Benchmark.ips do |x|
x.config(time: 10, warmup: 5)
x.report('sort_by_property_directly with sparse property') do
sort_by_property_directly(site_docs, "redirect_from".freeze)
end
x.report('schwartzian_transform with sparse property') do
schwartzian_transform(site_docs, "redirect_from".freeze)
end
x.compare!
end
# Next, test with a property they all have.
Benchmark.ips do |x|
x.config(time: 10, warmup: 5)
x.report('sort_by_property_directly with non-sparse property') do
sort_by_property_directly(site_docs, "title".freeze)
end
x.report('schwartzian_transform with non-sparse property') do
schwartzian_transform(site_docs, "title".freeze)
end
x.compare!
end
View
@@ -335,19 +335,26 @@ def inspect(input)
end
private
# Sort the input Enumerable by the given property.
# If the property doesn't exist, return the sort order respective of
# which item doesn't have the property.
# We also utilize the Schwartzian transform to make this more efficient.
def sort_input(input, property, order)
input.sort do |apple, orange|
apple_property = item_property(apple, property)
orange_property = item_property(orange, property)
if !apple_property.nil? && orange_property.nil?
- order
elsif apple_property.nil? && !orange_property.nil?
+ order
else
apple_property <=> orange_property
input.map { |item| [item_property(item, property), item] }
.sort! do |apple_info, orange_info|
apple_property = apple_info.first
orange_property = orange_info.first
if !apple_property.nil? && orange_property.nil?
- order
elsif apple_property.nil? && !orange_property.nil?
+ order
else
apple_property <=> orange_property
end
end
end
.map!(&:last)
end
private

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