Wednesday, May 26, 2010

My Regex Lessons (Probably 1 of many…)

OK, that previous post had a couple of minor problems.

First that regular expression – terribly unwieldy. I haven’t managed to shorten it fully yet, but this is marginally better:

"([\w\s:;… add whatever characters are valid here…]*)(?:\",|\"$)

Secondly, I wasn’t fully thinking through the matches/groups/captures hierarchy. I kept getting empty captures being reported back without understanding why I was getting them.

Updated code here:

open System
open System.Text.RegularExpressions

let (|ActiveRegex|_|) regex str =
let ms = Regex(regex).Matches(str)
if ms.Count > 0
then Some ((Seq.cast ms : Match seq))
else None

let matches s re =
match s with
| ActiveRegex re results -> results
| _ -> Seq.empty

let capturesSeq s p =
for m in matches s p ->
Seq.skip 1 (seq{for g in m.Groups -> g.Value})
|> Seq.concat

let csvRegex = "\"([\w\s:;~!@#$%\^&\*_<>,\.\\\/\|\[\]\{\}\(\)\-\+\?]*)(?:\",|\"$)"

let testLine = "\"31\",\"a 1\",\"b-2\",\"c+3\",\",.;~!@#$%^&*()\/?><,.|{}[]_+-\",\"\",\"14/05/2010 12:12:20 a.m.\",\"1: 2; 3. 4? 5[ 6] 7& 8*\",\"a,b\""

capturesSeq testLine csvRegex
|> Seq.iter (fun x -> printfn "%A" x)

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