01_assignment_benchmark.rb

require 'benchmark/ips'

def data
  Array.new(40000) do
    [ rand(-100..0), rand(0..100) ]
  end
end

def assign_destruct(data)
  data.map {|a| a[0] = a[0].abs.to_s; a }
end

def assign_nondestruct(data)
 data.map {|a| a = a.dup; a[0] = a[0].abs.to_s; a }
end

def splat(data)
  data.map {|first, *rest| [ first.abs.to_s, *rest ] }
end

Benchmark.ips do |x|
  x.report('assign destructive')    { assign_destruct(data) }
  x.report('assign nondestructive') { assign_nondestruct(data) }
  x.report('splat')                 { splat(data) }
  x.compare!
end

02_result.txt

Calculating -------------------------------------
   assign destructive    4.000  i/100ms
assign nondestructive    3.000  i/100ms
                splat    3.000  i/100ms
-------------------------------------------------
   assign destructive    46.936  (± 4.3%) i/s -    236.000
assign nondestructive    34.380  (± 5.8%) i/s -    174.000
                splat    32.821  (± 6.1%) i/s -    165.000

Comparison:
   assign destructive:   46.9 i/s
assign nondestructive:   34.4 i/s - 1.37x slower
                splat:   32.8 i/s - 1.43x slower

👍