Merge pull request #173 from styd/hash-slice

Native Hash#slice vs other slice alternatives

Author: Arcovion

README.md

@@ -937,6 +937,33 @@ Comparison:
          sort + to_h:    81972.8 i/s - 1.49x slower
 ```
 
+##### Native `Hash#slice` vs other slice implementations before native
+[code](code/hash/slice-native-vs-before-native.rb)
+
+Since ruby 2.5, Hash comes with a `slice` method to select hash members by keys.
+
+```
+$ ruby -v code/hash/slice-native-vs-before-native.rb
+ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux]
+Warming up --------------------------------------
+Hash#native-slice      178.077k i/100ms
+Array#each             124.311k i/100ms
+Array#each_w/_object   110.818k i/100ms
+Hash#select-include     66.972k i/100ms
+Calculating -------------------------------------
+Hash#native-slice         2.540M (± 1.5%) i/s -     12.822M in   5.049955s
+Array#each                1.614M (± 1.0%) i/s -      8.080M in   5.007925s
+Array#each_w/_object      1.353M (± 2.6%) i/s -      6.760M in   5.000441s
+Hash#select-include     760.944k (± 0.9%) i/s -      3.817M in   5.017123s
+
+Comparison:
+Hash#native-slice   :  2539515.5 i/s
+Array#each          :  1613665.5 i/s - 1.57x  slower
+Array#each_w/_object:  1352851.8 i/s - 1.88x  slower
+Hash#select-include :   760944.2 i/s - 3.34x  slower
+```
+
+
 ### Proc & Block
 
 ##### Block vs `Symbol#to_proc` [code](code/proc-and-block/block-vs-to_proc.rb)

code/hash/slice-native-vs-before-native.rb

@@ -0,0 +1,49 @@
+require 'benchmark/ips'
+
+HASH = {
+  title: "awesome",
+  description: "a description",
+  author: "styd",
+  published_at: Time.now
+}
+
+HASH.dup.each{ |k, v| HASH[:"other_#{k}"], HASH[:"more_#{k}"] = v, v }
+
+# Native implementation since v2.5
+#
+def fastest
+  HASH.slice(*%i[title author other])
+end
+
+# @ixti's faster implementation than that of ActiveSupport below
+#
+# Source:
+#   https://github.com/JuanitoFatas/fast-ruby/pull/173#issuecomment-470554483
+#
+def faster
+  memo = {}
+  %i[title author other].each { |k| memo[k] = HASH[k] if HASH.key?(k) }
+  memo
+end
+
+# ActiveSupport implementation of `slice` when it's not defined.
+#
+# Source:
+#   https://github.com/rails/rails/blob/01ae39660243bc5f0a986e20f9c9bff312b1b5f8/activesupport/lib/active_support/core_ext/hash/slice.rb#L24
+#
+def fast 
+  %i[title author other].each_with_object({}){ |k, h| h[k] = HASH[k] if HASH.key?(k) }
+end
+
+def slow
+  keys = %i[title author other]
+  HASH.select { |k, _| keys.include? k }
+end
+
+Benchmark.ips do |x|
+  x.report('Hash#native-slice   ') { fastest }
+  x.report('Array#each          ') { faster }
+  x.report('Array#each_w/_object') { fast }
+  x.report('Hash#select-include ') { slow }
+  x.compare!
+end