Question: I need a way to format numbers. I stored some numbers in my DB table, e.g. `12500`, and would like to print them in this format `12 500` (so there is a space every 3 digits). Is there an elegant way to do this?

Answer: 
Activesupport uses this regexp (and no reverse reverse).

```
10000000.to_s.gsub(/(\d)(?=(\d\d\d)+(?!\d))/, "\\1 ") #=> "10 000 000"

```
This is old but the fastest and most elegant way I could find to do this is:

```
def r_delim(s, e)                                                               
  (a = e%1000) > 0 ? r_delim(s, e/1000) : return; s << a                        
end

r_delim([], 1234567).join(',')

```

I'll try and add benchmarks at some point.