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Add Hash#values_at vs Array#map { Hash#[] } comparison #174

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Add Hash#values_at vs Array#map { Hash#[] } comparison #174

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450d9cb
Added: Hash#values_at vs Hash#slice#values.
kewlar Mar 14, 2019
47e9ce1
Change: add another slicing method, and add a note about assuming all…
kewlar Mar 21, 2019
2696656
Added: other methods of slicing Hash values, when keys may not exist.
kewlar Mar 21, 2019
4b5fa8b
Fix: file name for `Hash#slice#values` vs `Hash#values_at#compact` vs…
kewlar Mar 2, 2023
4d329bb
Change: remove edge cases form Hash#values_at.
kewlar Mar 2, 2023
9b9b274
Change: update benchmarks for code/hash/values_at-vs-map.rb
kewlar Mar 2, 2023
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20 changes: 20 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1038,6 +1038,26 @@ Array#each_w/_object: 1352851.8 i/s - 1.88x slower
Hash#select-include : 760944.2 i/s - 3.34x slower
```

##### `Hash#values_at` vs `Array#map { Hash#[] }`
[code](code/hash/values_at-vs-map.rb)

To select hash values by keys, when some of the keys may not exist in the hash,
and you care about the default values.

```
$ ruby -v code/hash/values_at-vs-map.rb
ruby 3.2.1 (2023-02-08 revision 31819e82c8) [x86_64-darwin22]
Warming up --------------------------------------
Hash#values_at 503.783k i/100ms
Array#map { Hash#[] } 279.576k i/100ms
Calculating -------------------------------------
Hash#values_at 4.901M (± 4.1%) i/s - 24.685M in 5.046090s
Array#map { Hash#[] } 2.801M (± 3.1%) i/s - 14.258M in 5.095692s

Comparison:
Hash#values_at : 4900567.9 i/s
Array#map { Hash#[] }: 2800981.4 i/s - 1.75x slower
```

### Proc & Block

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25 changes: 25 additions & 0 deletions code/hash/values_at-vs-map.rb
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@@ -0,0 +1,25 @@
require 'benchmark/ips'

HASH = {
a: 'foo',
b: 'bar',
c: 'baz',
d: 'qux'
}.freeze

# Some of the keys may not exist in the hash; we want to keep the default values.
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For existing keys, the benchmark does not change much.

# frozen_string_literal: true

require 'benchmark/ips'

HASH = {
  a: 'foo',
  b: 'bar',
  c: 'baz',
  d: 'qux'
}.freeze

# the keys exist in the hash
KEYS = %i[a b c d].freeze

def fastest
  HASH.values_at(*KEYS)
end

def slow
  HASH.fetch_values(*KEYS)
end

def slowest
  KEYS.map { |key| HASH[key] }
end

Benchmark.ips do |x|
  x.report('Hash#values_at       ') { fastest }
  x.report('Hash#fetch_values    ') { slow }
  x.report('Array#map { Hash#[] }') { slowest }
  x.compare!
end
ydakuka@yauhenid:~/ruby-docker-app$ docker run ruby-app  
Warming up --------------------------------------
Hash#values_at       
                       405.669k i/100ms
Hash#fetch_values    
                       354.263k i/100ms
Array#map { Hash#[] }
                       221.960k i/100ms
Calculating -------------------------------------
Hash#values_at       
                          4.191M (± 4.7%) i/s -     21.095M in   5.045130s
Hash#fetch_values    
                          3.895M (± 6.8%) i/s -     19.484M in   5.031663s
Array#map { Hash#[] }
                          2.429M (± 6.1%) i/s -     12.208M in   5.048470s

Comparison:
Hash#values_at       :  4190993.6 i/s
Hash#fetch_values    :  3894866.5 i/s - same-ish: difference falls within error
Array#map { Hash#[] }:  2429428.6 i/s - 1.73x  slower

KEYS = %i[a c e f].freeze

def fast
HASH.values_at(*KEYS)
end

def slow
KEYS.map { |key| HASH[key] }
end

Benchmark.ips do |x|
x.report('Hash#values_at ') { fast }
x.report('Array#map { Hash#[] }') { slow }
x.compare!
end