Re: st: problem with regexm leading to "regexp: unterminated ()" error for all observations

[Jamie Fagg <j.fagg@ich.ucl.ac.uk>]

Dear Phil Schumm, Nick Cox and Steve Samuels,

Many thanks for all your help on this.

Steve and Nick - thanks for the initial advice on what was causing the 
error.
Phil - I had just finished breaking it down when I saw your message. It 
is a much more elegant solution than the one I came up with after Nick 
recommended breaking it down, so thanks.
Best wishes,

Jamie

On 03/06/2011 18:10, Phil Schumm wrote:
> On Jun 3, 2011, at 7:35 AM, Jamie Fagg wrote:
> > I've a problem with the function -regexm-. I get the following message:
> >
> > regexp: unterminated ()
> <snip>
>
> > #delimit ;
> >
> > //regular expression to define whether postcode is syntactically correct
> >
> > ge postcodevalid = 1 if regexm(postcode,"(GIR 
> > 0AA)|(((A[BL]|B[ABDHLNRSTX]
> > ?|C[ABFHMORTVW]|D[ADEGHLNTY]|E[HNX]?|F[KY]|G[LUY]?|H[ADGPRSUX]
> > |I[GMPV]|JE|K[ATWY]|L[ADELNSU]?|M[EKL]?|N[EGNPRW]?|O[LX]|P[AEHLOR]
> > |R[GHM]|S[AEGKLMNOPRSTY]?|T[ADFNQRSW]|UB|W[ADFNRSV]|YO|ZE)[1-9]?[0-9]
> > |((E|N|NW|SE|SW|W)1|EC[1-4]|WC[12])[A-HJKMNPR-Y]|(SW|W)([2-9]|[1-9]
> > [0-9])|EC[1-9][0-9]) [0-9][ABD-HJLNP-UW-Z]{2})")==1;
>
> I'm not sure why Stata chokes on this, though I would suspect it might 
> have something to do with the length.  As Nick and Steven have already 
> noted, the repeat qualifier {n} is not supported by Stata's regular 
> expression syntax, so you'll need to replace
>
>     [ABD-HJLNP-UW-Z]{2}
>
>
> with the equivalent
>
>
>     [ABD-HJLNP-UW-Z][ABD-HJLNP-UW-Z]
>
>
> Now, Nick suggested breaking the expression up, so let's do that.  
> Your expression is equal to
>
>     (p1)|(((p2a1a|p2a1b|p2a1c)p2a1d|p2a2|p2a3|p2a4)p2b)
>
>
> where the individual parts (as assigned to Stata macros) are
>
>
>     loc p1    "GIR 0AA"
>     loc p2a1a 
> "A[BL]|B[ABDHLNRSTX]?|C[ABFHMORTVW]|D[ADEGHLNTY]|E[HNX]?|F[KY]|G[LUY]?"
>     loc p2a1b 
> "H[ADGPRSUX]|I[GMPV]|JE|K[ATWY]|L[ADELNSU]?|M[EKL]?|N[EGNPRW]?|O[LX]"
>     loc p2a1c 
> "P[AEHLOR]|R[GHM]|S[AEGKLMNOPRSTY]?|T[ADFNQRSW]|UB|W[ADFNRSV]|YO|ZE"
>     loc p2a1d "[1-9]?[0-9]"
>     loc p2a2  "((E|N|NW|SE|SW|W)1|EC[1-4]|WC[12])[A-HJKMNPR-Y]"
>     loc p2a3  "(SW|W)([2-9]|[1-9][0-9])"
>     loc p2a4  "EC[1-9][0-9]"
>     loc p2b   " [0-9][ABD-HJLNP-UW-Z][ABD-HJLNP-UW-Z]"
>
>
> This may then be easily broken up as follows:
>
>
>     gen byte valid = regexm(postcode,"`p1'")
>     replace valid = 1 if regexm(postcode,"`p2a1a'`p2a1d'`p2b'")
>     replace valid = 1 if regexm(postcode,"`p2a1b'`p2a1d'`p2b'")
>     replace valid = 1 if regexm(postcode,"`p2a1c'`p2a1d'`p2b'")
>     replace valid = 1 if regexm(postcode,"(`p2a2'|`p2a3'|`p2a4')`p2b'")
>
>
> -- Phil
>
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