Inserting a space in between characters using gsub - Ruby

Question

Let's say I had a string "I have 36 dogs in 54 of my houses in 24 countries". Is it possible by using only gsub to add a " " between each digit so that the string becomes "I have 3 6 dogs in 5 4 of my houses in 2 4 countries"?

gsub(/(\\d)(\\d)/, "#{$1} #{$2}") does not work as it replaces each digit with a space and neither does gsub(/\\d\\d/, "\\d \\d") , which replaces the each digit with d .

Answer 1

s = "I have 3651 dogs in 24 countries"

Four ways to use String#gsub :

Use a positive lookahead and capture group

r = /
    (\d)   # match a digit in capture group 1
    (?=\d) # match a digit in a positive lookahead
    /x     # extended mode

s.gsub(r, '\1 ')
  #=> "I have 3 6 5 1 dogs in 2 4 countries"

A positive lookbehind could be used as well:

s.gsub(/(?<=\d)(\d)/, ' \1')

Use a block

s.gsub(/\d+/) { |s| s.chars.join(' ') }
  #=> "I have 3 6 5 1 dogs in 2 4 countries"

Use a positive lookahead and a block

s.gsub(/\d(?=\d)/) { |s| s + ' ' }
  #=> "I have 3 6 5 1 dogs in 2 4 countries"

Use a hash

h = '0'.upto('9').each_with_object({}) { |s,h| h[s] = s + ' ' }
  #=> {"0"=>"0 ", "1"=>"1 ", "2"=>"2 ", "3"=>"3 ", "4"=>"4 ",
  #    "5"=>"5 ", "6"=>"6 ", "7"=>"7 ", "8"=>"8 ", "9"=>"9 "} 
s.gsub(/\d(?=\d)/, h)
  #=> "I have 3 6 5 1 dogs in 2 4 countries" 

Answer 2

An alternative way is to look for the place between the numbers using lookahead and lookbehind and then just replace that with a space.

[1] pry(main)> s = "I have 36 dogs in 54 of my houses in 24 countries"
=> "I have 36 dogs in 54 of my houses in 24 countries"
[2] pry(main)> s.gsub(/(?<=\d)(?=\d)/, ' ')
=> "I have 3 6 dogs in 5 4 of my houses in 2 4 countries"

Answer 3

In order to reference a match you should use \\n where n is the match, not $1 .

s = "I have 36 dogs in 54 of my houses in 24 countries"
s.gsub(/(\d)(\d)/, '\1 \2') 
# => "I have 3 6 dogs in 5 4 of my houses in 2 4 countries"