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MathGroup Archive 2002

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Pattern matching

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33912] Pattern matching
  • From: John Leary <leary at paradise.net.nz>
  • Date: Tue, 23 Apr 2002 07:13:22 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Greetings

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[listTemplates]}]

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.


I would be very grateful for your help.


Regards

John Leary




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