Re: Pattern matching
- To: mathgroup at smc.vnet.net
- Subject: [mg33965] Re: [mg33912] Pattern matching
- From: BobHanlon at aol.com
- Date: Wed, 24 Apr 2002 01:23:02 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 4/23/02 9:39:43 AM, leary at paradise.net.nz writes:
>Can you help me please - there must be a simple solution to this problem,
>
>but I can't find it.
>
> From a list of character strings and a list of templates, I need to
>produce a list of all strings that match any of the templates. For example:
>
>listData={"18K0F3C--" , "2K40GXX--" , "400HGXX--" , "5M00G1F--" ,
"960KG1D--"}
>listTemplates={"???H?????" , "???K?????"}
>result={"400HGXX--","960KG1D--"}
>
>In the templates, ? is a wild-card that represents a single character.
>The data strings contain only alpha-numeric characters and hyphens - no
>
>other characters.
>There are no special requirements for the result: duplication and random
>
>order are acceptable.
>
>
>I searched the MathGroup archive and found a very useful function that
>does
>exactly what I want, but it works only on individual strings, not lists
>of
>strings (msg00051):
>
>QMMatchQ[s_String, p_String] := MatchQ[Characters[s], Characters[p] /.
>"?"
>-> _ ]
>
>
>
>I tried to use it in the following way, but the result is a list of the
>
>matching templates, not the matching strings :
>
>QMMatchQ[s_String, p_String] := MatchQ[Characters[s], Characters[p] /.
>"?"
>-> _ ]
>SetOptions[Intersection, SameTest -> (QMMatchQ[#1,#2]& )];
>result=Intersection[listData,listTemplates]
>{"???H?????","???K?????"}
>
>
>It ought to be a small step from there to the result that I need, but I
>
>can't find a simple solution.
>
>One alternative approach would be a Do loop:
>
>b={};
>Do[b=Append[b,Select[listData,QMMatchQ[#,listTemplates[[n]]]&]],{n,1,Length[l
istTemplates]}]
>
>This works but seems to be very slow for large lists. In the real case,
>
>listData can be very large - up to 250,000 elements - and the Do loop
>approach doesn't seem to be optimum.
listData={"18K0F3C--","2K40GXX--",
"400HGXX--","5M00G1F--","960KG1D--"};
listTemplates={"???H?????","???K?????"};
Clear[QMMatchQ];
QMMatchQ[s_String,{p__String}]:=Or @@
(MatchQ[Characters[s],
Characters[#]/."?"->_]& /@ {p});
Select[listData,
QMMatchQ[#,listTemplates]&]
{"400HGXX--", "960KG1D--"}
or
Cases[listData,
_?(QMMatchQ[#,listTemplates]&)]
{"400HGXX--", "960KG1D--"}
Bob Hanlon
Chantilly, VA USA