Bug #15929: Array#minmax is much slower than calling both #min and #max

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 2.7.0dev
• Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN

[janosch-x (Janosch Müller)]

this is similar to issue 15807 about Ranges and maybe also to 13917

current situation:

• calling Array#minmax incurs a performance penalty of almost 50% compared to calling both #min and #max

require 'benchmark/ips'
arr = (1..1000).map { rand }
Benchmark.ips do |x|
  x.report('min, max') { [arr.min, arr.max] }
  x.report('minmax')   { arr.minmax }
end

min, max  53.832k (± 1.8%) i/s -  270.861k in 5.033263s
  minmax  30.093k (± 1.2%) i/s -  151.980k in 5.051078s

background:

• #minmax is included via Enumerable
• Enumerable#minmax does not call array's optimized #min and #max implementations

possible solutions:

• a) change Enumerable#minmax and let it rb_funcall min and max as suggested here (will also fix 15807)
• b) implement minmax in array.c to call rb_ary_min and rb_ary_max

[jeremyevans0 (Jeremy Evans)]

• File array-minmax.patch array-minmax.patch added

janosch-x (Janosch Müller) wrote:

possible solutions:

• a) change Enumerable#minmax and let it rb_funcall min and max as suggested here (will also fix 15807)

We cannot use this approach. Enumerable#each can have side effects, and you cannot iterate twice for minmax in the general case. Consider:

File.open('...', &:minmax)

• b) implement minmax in array.c to call rb_ary_min and rb_ary_max

I think this is the correct approach in Array and any other class that overrides min/max. Attached is a patch that implements it.

[janosch-x (Janosch Müller)]

jeremyevans0 (Jeremy Evans) wrote:

We cannot use this approach. [...]

I see, thanks for the explanation!

• Status changed from Open to Closed

Applied in changeset git|ced640951b0e7164a12ea1770330eba3e6109fc2.

---

Implement Array#minmax

Array#minmax was previous not implemented, so calling #minmax on
array was actually calling Enumerable#minmax. This is a simple
implementation of #minmax by just calling rb_ary_min and
rb_ary_max, which improves performance significantly.

Fixes [Bug #15929]