Re: Capture patterns

["Eric Tetz" <erictetz@...>]

On Jan 8, 2008 7:04 AM, Jeff Wise <jwise@sealyrealty.com> wrote:
> Look at all these possible formats:
>
> 1. $100.00
> 2. .00
> 3. 100,000.00
> 4. -1,234.56
> 5. (1,234.56)
> 6. 1,234.56CR
> 7. 1,234.56-
> 8. +100.00

If you strip out the superfluous characters:

  input = string.gsub(input, "[$,%+%s]", "")

It reduces the number of formats to 6.

One approach is just to try every valid pattern until one sticks:

   -- I have no idea what 'CR' appended to a number means,
   -- so I'll pretend it means negative...

   function match_number(s)
      s = s:gsub("[$,+%s]", "") -- strip garbage
      local n =
            s:match("%-(%d+%.%d+)")    -- -22.22
         or s:match("(%d+%.%d+)%-")    -- 22.22-
         or s:match("%((%d+%.%d+)%)")  -- (22.22)
         or s:match("(%d+%.%d+)CR")    -- 22.22CR
      return n and -n
          or s:match("(%d+%.%d+)")     -- 22.22
          or s:match("(%.%d+)")        --   .22
   end

Or you could use one pattern and test if you caught any of the extra stuff:

   function match_number(s)
      s = s:gsub("[$,+%s]", "") -- strip garbage
      local pre, n, post = s:match("([-(]?)(%d*%.%d+)([CR-]?)")
      return (pre ~= "" or post ~= "") and -n or n
   end

I'm sure there are a dozen other ways to skin this cat, but I've gotta
get to work...

> I think that the section could be better
> organized by covering the "magic characters" in
> order instead of randomly.  This would make the
> text more useful as a reference

Check out the online manual. It has exactly what you want. :)

Cheers,
Eric