Fastest way to retrive all numbers from a string

string_scan_benchmark.rb

# Code mostly adapted from original by Jesus: https://www.ruby-forum.com/t/extract-numbers-from-string/115434/5

require 'benchmark'

n = 100_000
header = 't=1570633834.463123'

Benchmark.bmbm do |x|
  x.report('scan') do
    n.times {header.scan(/\d/).join}
  end
  x.report('gsub') do
    n.times {header.gsub(/[^\d]/,'')}
  end
  x.report('gsub2') do
    n.times {header.gsub(/\D/, '')}
  end
  x.report('tr') do
    n.times {header.tr('^0-9','')}
  end
  x.report('delete') do
    n.times {header.delete('^0-9')}
  end
  x.report('split') do
    n.times {header.split(/[^\d]/).join}
  end
end;

# Memory benchmark using `benchmark-memory` gem: https://github.com/michaelherold/benchmark-memory

require 'benchmark/memory'

Benchmark.memory do |x|
  x.report('scan') do
    header.scan(/\d/).join
  end
  x.report('gsub') do
    header.gsub(/[^\d]/,'')
  end
  x.report('gsub2') do
    header.gsub(/\D/, '')
  end
  x.report('tr') do
    header.tr('^0-9','')
  end
  x.report('delete') do
    header.delete('^0-9')
  end
  x.report('split') do
    header.split(/[^\d]/).join
  end

  x.compare!
end;

### OUTPUT ###

Rehearsal ------------------------------------------
scan     0.501514   0.001129   0.502643 (  0.503412)
gsub     0.212457   0.001135   0.213592 (  0.213919)
gsub2    0.215123   0.001258   0.216381 (  0.217076)
tr       0.039926   0.000275   0.040201 (  0.040221)
delete   0.036174   0.000069   0.036243 (  0.036440)
split    0.238501   0.001149   0.239650 (  0.239973)
--------------------------------- total: 1.248710sec

             user     system      total        real
scan     0.476308   0.000484   0.476792 (  0.477103)
gsub     0.210125   0.000944   0.211069 (  0.211373)
gsub2    0.206936   0.001010   0.207946 (  0.208079)
tr       0.037802   0.000043   0.037845 (  0.037923)
delete   0.034158   0.000052   0.034210 (  0.034314)
split    0.233673   0.001042   0.234715 (  0.235123)

Calculating -------------------------------------
                scan     1.608k memsize (   320.000  retained)
                        21.000  objects (     2.000  retained)
                        11.000  strings (     1.000  retained)
                gsub   568.000  memsize (   320.000  retained)
                         5.000  objects (     2.000  retained)
                         3.000  strings (     1.000  retained)
               gsub2   568.000  memsize (   320.000  retained)
                         5.000  objects (     2.000  retained)
                         3.000  strings (     1.000  retained)
                  tr   120.000  memsize (     0.000  retained)
                         3.000  objects (     0.000  retained)
                         3.000  strings (     0.000  retained)
              delete    80.000  memsize (     0.000  retained)
                         2.000  objects (     0.000  retained)
                         2.000  strings (     0.000  retained)
               split   648.000  memsize (     0.000  retained)
                         9.000  objects (     0.000  retained)
                         5.000  strings (     0.000  retained)

Comparison:
              delete:         80 allocated
                  tr:        120 allocated - 1.50x more
                gsub:        568 allocated - 7.10x more
               gsub2:        568 allocated - 7.10x more
               split:        648 allocated - 8.10x more
                scan:       1608 allocated - 20.10x more