Format an integer with commas to make it more readable (See related posts)

More information or better ways of doing this welcome ...

def commify(number)
    c = { :value => "", :length => 0 }
    r = number.to_s.reverse.split("").inject(c) do |t, e|  
      iv, il = t[:value], t[:length]
      iv += ',' if il % 3 == 0 && il != 0    
      { :value => iv + e, :length => il + 1 }
    end
    r[:value].reverse!
  end

Alex Young suggested

def commify(v)
 (s=v.to_s;x=s.length;s).rjust(x+(3-(x%3))).scan(/.{3}/).join(',').strip
end

and there's always

number_with_delimiter(number, delimiter)

from NumberHelper in the Rails API ... which is implemented as follows:-

def number_with_delimiter(number, delimiter=",")
  number.to_s.gsub(/(\d)(?=(\d\d\d)+(?!\d))/, "\\1#{delimiter}")
end

They don't always work too well when the number has a decimal point in it (and more than two or so digits after the decimal point), so there's room for an improved version ...

JV suggested the following snippet from http://pleac.sourceforge.net/pleac_ruby/numbers.html which appears to be able to handle commas and decimal places as well.

def commify(n)
    n.to_s =~ /([^\.]*)(\..*)?/
    int, dec = $1.reverse, $2 ? $2 : ""
    while int.gsub!(/(,|\.|^)(\d{3})(\d)/, '\1\2,\3')
    end
    int.reverse + dec
end