Hash#merge({}) vs Hash#dup#merge!({}) vs {}#merge!(Hash)

[bejmuller]

In some cases we want duplicates of hashes to be created while merging, so I was wondering which one is the fastest way of achieving this:

$ ruby -v code/hash/merge-vs-dup-merge-bang-vs-merge-bang.rb ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-linux]
Calculating -------------------------------------
Hash#merge({}) 603.000 i/100ms
Hash#dup#merge!({}) 650.000 i/100ms
{}#merge!(Hash) 1.763k i/100ms
-------------------------------------------------
Hash#merge({}) 6.593k (± 7.6%) i/s - 33.165k
Hash#dup#merge!({}) 6.591k (± 5.2%) i/s - 33.150k
{}#merge!(Hash) 17.654k (± 3.0%) i/s - 89.913k
Comparison:
{}#merge!(Hash): 17654.0 i/s
Hash#merge({}): 6592.7 i/s - 2.68x slower
Hash#dup#merge!({}): 6591.2 i/s - 2.68x slower

[JuanitoFatas]

Thanks for the patch! I think dup#merge! you can just use Hash#merge. And it is covered by https://github.com/JuanitoFatas/fast-ruby#hashmerge-vs-hashmerge-code. Close this one.

Thanks again!

[bejmuller]

The reason of opening this PR was to show the difference between {}#merge!(Hash) vs Hash#merge({}) which is NOT covered anywhere in this repo.

dup.merge! was just added as a third option (which sometimes is used)

I would have appreciated a comment first, and a possibility to reply before closing it right away...

[JuanitoFatas]

The reason of opening this PR was to show the difference between {}#merge!(Hash) vs Hash#merge({}) which is NOT covered anywhere in this repo.

👍

I would have appreciated a comment first, and a possibility to reply before closing it right away...

My apologies.

[bejmuller]

No problem :) The description and the title I gave it are not the best, so that could have caused some confusion.

[JuanitoFatas]

Thank you Elod! I merged your commits in d83756f and made some minor changes 🙇

Thank you for your contribution 👍 🌠 🌠 🌠 🌠 🌠

[krzysiek1507]

{}#merge!(other) do end is the fastest only when other has only one key.
Every key more means 10% slow down.

ENUM=(1..100)ORIGINAL_HASH={foo: {a: 1,b: {c: 3}},bar: {},baz: "baz",ruby: "ruby",test: "test",yup: "yup",rails: "rails"}deffastENUM.inject([])do |accumulator,element|
accumulator << ({bar: element}.merge!(ORIGINAL_HASH){ |_key,left,_right| left})endenddefslowENUM.inject([])do |accumulator,element|
accumulator << ORIGINAL_HASH.merge(bar: element)endenddefslow_dupENUM.inject([])do |accumulator,element|
accumulator << ORIGINAL_HASH.dup.merge!(bar: element)endendBenchmark.ipsdo |x|
x.report("{}#merge!(Hash) do end"){fast}x.report("Hash#merge({})"){slow}x.report("Hash#dup#merge!({})"){slow_dup}x.compare!endruby2.6.0p0(2018-12-25revision66547)[x86_64-darwin18]Warmingup --------------------------------------
{}#merge!(Hash) do end1.799k i/100msHash#merge({}) 2.956k i/100msHash#dup#merge!({}) 1.217k i/100msCalculating -------------------------------------
{}#merge!(Hash) do end18.216k(±1.7%) i/s - 91.749kin5.038319sHash#merge({}) 29.844k (± 2.9%) i/s - 150.756k in 5.056616sHash#dup#merge!({}) 12.288k (± 2.4%) i/s - 62.067k in 5.054204sComparison:
Hash#merge({}): 29844.0 i/s{}#merge!(Hash) do end: 18215.6 i/s - 1.64x slowerHash#dup#merge!({}): 12287.7 i/s - 2.43x slower